The Saiyans of the Dragon Ball franchise were a bunch of Blood Knight barbarians that wiped out the more advanced Tuffles who shared their homeworld. All of their technology was either salvaged from what was left of the Tuffles' civilization or given to them when Frieza recruited them into his planet-broker business.
The Zentraedi of the Super Dimension Fortress Macross franchise are somewhat this when introduced. While they have and can operate their machinery, they have no knowledge of how to repair it or build anything new with the technology, beyond what the automated factories spit out. It makes sense in context for the series, since the Protoculture made them for war and this lack of knowledge would make it less likely for the Zentraedi to rebel.
The Abductors from Jhonen Vasquez's Squee! series. They later pop up in an episode of Invader Zim.
This is how the Kree/Skrull war got started! The already-advanced Skrulls visited the Kree homeworld to see if they were developed enough to join the Skrull trade empire; they were prepared to share their tech, but only with the superior species of the planet. Unfortunately, the human-like Kree shared their world with the equally intelligent plants, the Cotati. So the Skrulls held a contest to see who was more creative, and the Kree lost. The Kree went "Oh yeah?!!", killed the still-peaceful Skrulls and paperclipped their technology. By the time the Skrull empire finally responded (their homeworld being in the Andromeda galaxy), the Kree had already advanced enough to be able to match them in space warfare.
The Vespa in Irredeemable use teleportation technology given to them by Hornet as part of a deal he made with them to great effect as a weapon. But they don't know how it works as well as its creator Qubit. Qubit eventually uses his superior understanding of the technology to take it away from the Vespa.
In the MST3K'd classic Prince of Space, the chicken-nosed invaders are capable of interplanetary travel, but invade Earth because their fuel is less efficient than something invented in Japan in the 50's (in fact their entire plan is based around stealing it from Earth so the next generation of ships can actually invade). Also, their weapons don't work on garishly dressed heroes who wave batons.
The "Prawns" of District 9. Whilst they possess high levels of technology, it isn't clear that they developed it themselves and when found aboard their mothership are in a very poor state of health and hygiene. After (nominal) incorporation into human society, they rank very much as second-class citizens and barely above animals. This is the cause of much speculation in-universe, the leading idea being the leadership caste was wiped out.
The Tenctonese from Alien Nation were a slave race who overthrew their masters and landed their ship on Earth (presumably, then, the vast majority of their people are still slaves). They are very adaptable, but this means they end up about as advanced as the humans they live amongst.
Planet 51 is set on an alien world, styled after 1950s-era suburban America. Though they have ray guns and hovering cars, their knowledge of the universe is comically outdated (they think the universe is only 500 miles long), and, as far as one can tell, they have no knowledge of space travel.
Aliens in Signs. Their spacecraft possess the ability to travel vast interstellar distances (to Earth), and also exhibit the ability to cloak their spacecraft with a sort of invisibility shield. They, however, may not possess the astronomical skills to observe that over 70% of the Earth's surface is covered by water, a reasonably common substance that is instantly fatal to them. Furthermore, the aliens are never seen using any sorts of projectiles/energy weapons, and they appear to be completely naked. Not only would bodies of water be immediately fatal, but simple contact with water vapor in the air should have rendered it impossible for them to wander around Earth's surface. Reality Ensues when the invasion is defeated almost immediately.
The theory of this is put forth in ET, as Elliot's brother thinks the titular alien may just be a worker drone, and isn't necessarily a great scientist or anything. ET is actually a botanist, but has more than enough engineering know-how to make a communication device. Then again, he ran away screaming when a can of pencils fell over and the kids did initially think he was a hairless monkey.
Pretty much everybody in space, from the human point of view, in Harry Turtledove's "The Road Not Taken". Gravity manipulation and hyperdrive are easy to create — but if you do so before coming up with the scientific method, they'll skew your whole technology. The aliens who invaded mid-21st-Century Earth had the tech level (and mindset) of Spanish conquistadors. They tried to intimidate us with arquebuses ... and the U.S. National Guard mopped the floor with them.
There was a sequel where humanity had also become stagnant at just about the 2039 tech level once they conquered the stars, then encountered another interstellar empire that had also never discovered the simple trick at all, and were thus much more advanced. They saw humans as this.
The Lizards in World War/Colonization series have interstellar travel, but their weapons technology is about where humans were at the end of the twentieth century, and they're so conservative that they are pretty much incapable of improving it, or adapting their tactics to match rapidly advancing human technology, so we catch up with them pretty quickly when they invade in the middle of WWII. It's implied in the books that the Lizards' weapons technology isn't as advanced as their space technology because they've been at peace with themselves for thousands of years, and the other two races they conquered weren't much more advanced than Medieval Europe, so they had no need to innovate further.
The Fithp from Larry Niven and Jerry Pournelle's novel Footfall. If they hadn't had a Precursor artifact handy to tell them how to build stuff, they probably would still have been at the hunter-gatherer stage of civilization.
Most of the races in David Brin's Uplift universe. Like the Fithp, they rely entirely on technologies and knowledge handed down through generations of civilizations, and most never actually evolve on their own terms and time schedule. In fact, many see it as blasphemy.
The Howlers from Animorphs have advanced weaponry and interstellar spaceships despite being mentally children. Justified in that they were artificially created by an Eldritch Abomination for the purpose of killing as many sentient species as possible. Also, the Yeerks were still in the Stone Age when they stole interstellar spaceships from Andalite outposts and began to spread throughout the galaxy. By the time they reach Earth though, they've had twenty-odd years to develop their own technology and the Schizo Tech is not obvious.
In K. A. Applegate's Remnants series, the Shipwrights seem to be the only species that managed to develop advanced technology; the Children and the Squids were created by them and inherited their stuff, while no explanation is ever given for how the Riders got their cool hovering surfboards. And of course, humans eventually come into possession of this cool stuff too.
In Everworld, there is an alien race known as the Coo-Hatch. Although they possess the ability to forge objects out of a nigh-unbreakable steel capable of cutting through any known material with little effort, the rest of their technological base leaves a lot to be desired. A high school chemistry textbook blows their minds and also allows them to develop gunpowder, which was previously undiscovered by them. Even something as simple as knot-tying and the use of a pulley system is beyond them.
Humans in Frederik Pohl's Heechee Saga use abandoned Heechee technology to explore the galaxy without really knowing how it works.
The Kzin from Larry Niven's Known Space universe, particularly during the Man-Kzin Wars, who culturally resemble a hybrid of lions and Apache/Viking/Zulus more than they do a species with a thriving inter-stellar empire. Justified, as spacefaring Kzinti were a backward isolated stone-age tribe that got their technology from another species (herbivore traders who were hiring them to be their strong-arm army). The Kzinti then turned around and wiped out the more advanced members of their species, enslaved their benefactors, and started a religious crusade of galactic conquest. Big on ambitions, small on planning. Known Space is fueled by this trope. The Puppeteers use periodic transfers of Sufficiently Advanced Technology to manipulate the less advanced races (like the Kzin and humans) into participating in their master plan.
The title beings in Stephen King's The Tommyknockers are an odd example. It's unclear how much of the principles behind their technology they actually understand, but what is clear is that they're technically advanced but dumb in a lot of common-sense ways, and a lot of their high-tech solutions are Awesome but Impractical at best. For example, they run their entire operation off of AA, AAA, and C- and D-cell batteries with the occasional forsakenLiving Battery as a supplement and even go so far as to send two of their own on a Suicide Mission into a hostile atmosphere to get more rather than rely on the electric grid. It simply never occurs to any of them to just buy a goddamn AC/DC converter. Their violent tempers don't help either: When their stupidity regarding the batteries is pointed out, they explode because they never thought of it.
The Phinons in Dykstra's War use technology that seems very counterintuitive in its design, and there appears to be no way to negotiate with them. The reason turns out to be that they have barely animal intelligence. They evolved spacecraft-building the same way bees evolved to build hives or beavers to build dams. It's a very good design, certainly good enough to kill any nascent competitor spacefaring species like humanity before we can develop more advanced tech ourselves. But the Phinons themselves are virtually mindless.
The Star TreknovelIshmael by Barbara Hambly asserts that the Klingons were a primitive race who were conquered by starfarers called the Karsids. The Klingons, being Klingons, then defeated the Karsids and appropriated all their tech, giving them advanced tech despite still being culturally barbaric, a perfect object lesson in the worth of the Prime Directive.
Subverted, in that the Klingons did eventually figure out how to build and maintain this technology on their own to the point that they can manage a sizeable stellar empire and stay at par with the Federation and the Romulans. However, they remain frozen culturally at their initial primitive level.
Poul Anderson's Dominic Flandry series has many examples of "barbarians" — primitive alien species given spaceships and high-tech weaponry by a more advanced civilization, generally for use as expendable mercenaries and deniable proxies.
In Empire from the Ashes, one of the perplexing aspects of the genocidal Achuultani invaders is the odd patchwork their ships exhibit, mixing superior and inferior technologies in defiance of what the natural progression of technology should have resulted in. For instance, "they appear to possess only a very rudimentary appreciation of gravitonics and their ships do not employ gravitonic sublight drives, yet their sublight missiles employ a highly sophisticated gravitonic drive which is, in fact, superior to that of the Imperium." It is later theorized that the ships were deliberately handicapped by their overlord AI, thus perpetuating the "crisis" that enables it to exercise emergency protocols to maintain control.
In Poul Anderson's The High Crusade, humans. An alien spaceship lands on Earth in the 1300s, and the locals manage to kill all the invaders save a single captive. They load their army onto the ship, fly out, lose track of Earth, and manage to dismantle the alien empire.
The Byrum of Stephen King's Dreamcatcher are infectious spores that come to Earth in ships from a race they presumably were able to invade, though the success of even that invasion is questionable.
The Gbaba in David Weber's Safehold novels almost qualify. Their technology had been stagnant for at least two thousand years when humanity found them, and had humanity gotten another 50 years to innovate before the war, the Gbaba would have lost. Since all evidence suggests they aren't likely to develop any new technology while humanity hides and rebuilds, Merlin is working hard to bring the people of Safehold up to a technological level capable of making the Gbaba qualify for this trope when round 2 comes along.
In Timothy Zahn's Blackcollar series, the Ryqril aliens are much more powerful than humanity and other species, but their technology all comes from other enslaved races - they are incapable of building it themselves, or advancing it. It ends up being a big problem for them when they have to fight human guerrillas who are aware of this.
Christopher Anvil's Pandora Planet novels are based on this: while the aliens who invade Earth have higher tech, and their leaders are very, very smart, on average the typical alien isn't as bright as the typical human. Combined with the human knowledge and experience of warfare (barbed wire is a horror the aliens have never seen before, and their commander is appalled to receive reports about humans standing around laughing at them in the middle of battles due to the invaders' ineptitude), the leaders quickly reach an accommodation with humanity and bring them aboard as partners. Except not quite: the early accommodation is designed to release Earth ideas over a limited area of the alien empire, to allow the alien leaders to find the best human ideas - the 'hope' of all the ideas from Pandora's Planet - and humans to bring into the empire's leadership. At one early point, the technological level of Earth humans is stated to be "0.9 Centra-level, in some respects higher". As is soon made clear, the "in some respects higher" is not just referring to military technology. It is also made clear early on how the Centrans are in space, while the Earth humans aren't: humans simply haven't gotten around to discovering the necessary theories behind the interstellar drive, while the Centrans have known them for quite some time.
An odd mish-mash in David Gemmell's Echoes of the Great Song. Although called magic, the ruling Avatars have effectively laser weapons but no good way of recharging them. They use these to dominate the humans who are at an Ancient Rome sort of level. An invasion force arrives by teleporting in a huge chunk of rock but fight using black powder muskets.
In Terry Pratchett and Steve Baxter's The Long Earth it seems that having the natural ability to Step between alternate Earth's retards a race's technical prowess. Of the various races and subraces of "elves" and "trolls" met by Lobsang and Joshua in their voyage across the Long Earth none seem to have gotten beyond the Neolithic era of development. They, especially Joshua worry what will happen when the migrating hordes meet up with humans, who have discovered a technological method of dimension travel and are colonizing in the opposite direction of the migration. Hint: The next book is called The Long War.
Humans effectively start out as this in the earliest story arc or two of Perry Rhodan. Having barely managed to land the first man on the moon, Earth's first faster-than-light vessel is an auxiliary craft of the alien cruiser stranded there, soon after replaced by the alien battleship that destroyed it on its first expedition outside the solar system. However, humanity also put considerable effort into avoiding being this trope for long here, doing its level best to work on closing the technology gap and keep the position of its homeworld as secret as at all possible in the meantime.
Deathscent by Robin Jarvis sees Elizabethan-era humanity uplifted by mysterious "Special Ambassadors". Everyone now lives in a network of domed islands floating in space, with greatly-extended lifespans and Clock Punk livestock that chew up plants to produce food. The Ambassadors are assumed to be angels and no-one truly understands their technology, even though they haven't visited in ages. They've been hunted to extinction by the Iribeans. Evil! Brindle gloats that the whole thing is a pretty zoo with humankind as the star attraction.
In Terry Pratchett's The Last Hero, Ankh-Morpork devises the Disc's first spaceship - or at least the first one capable of returning. A bewildering amalgam of basic physics, magic and carpentry, it is made out of wood and powered by dragons. (A Shout-Out to Baron von Munchausen).
the Krullians also devised spacecraft. Unfortunately, as they lived on the edge of a flat earth, their launch philosophy was to tip it over the rim and hope the supporting cable and winch were strong enough to be able to haul it back.
The Pakleds from the Star Trek: The Next Generation episode "Samaritan Snare" appeared to be functionally retarded, but managed to steal enough technology from their neighbours to maintain a rather patchwork starflight capability. It isn't clear if this is a racial characteristic or just the few featured in the episode, since the ones that appear as extras in later seasons appear to mechanics and merchants.
Same with the Kazon from Voyager, who have interstellar spaceflight forcibly appropriated from their Trabe conquerors, but can't figure out how to synthesize water...
Another from Voyager: the Vidiians are suffering from the 'phage', a disease which destroys their internal organs. They are able to steal organs from every other sentient race for transplant with no risk of rejection, a feat which even current Federation medical science cannot replicate. Despite this, they seem unable to actually cure the phage to begin with. It seems hard to believe that the Vidiians have no knowledge of virology or immunology given that preventing organ rejection requires knowledge of immunology to begin with—more likely the writers decided not to research the matter.
At one point it's revealed that Klingon tissue is resistant to the phage, setting up a plotline putting half-Klingon B'lanna Torres in jeopardy of being harvested—never mind that a simple tissue sample, along with cloning technology, would be all that the Vidiians would need. Both are within 20th century technology, let alone what the Federation has available, and yet this win-win (the Vidiians cure the phage without harvesting B'lanna, and Voyager gets a valuable ally in return) never occurs to anyone involved. Worse still, there was one point where the Vidiians kidnapped B'lanna and somehow physically split her into her component human and Klingon halves. If you can do that, surely you could have just taken a blood sample and made yourself a full-Klingon B'lanna without all the fuss.
The Bajorans have supposedly tens of thousands of years of recorded history, including the best part of a millenium of manned spaceflight, at the very least. But their technology seems to have stagnated at some point and most of the people behave like Medieval peasant stereotypes. Of course the the fact that their religion is based around worshipping Sufficiently Advanced Aliens might have something to do with this. The whole thing with the Cardassians going all Holocausty on them probably didn't help either.
The Suliban on Star Trek: Enterprise also count. Phlox has encountered them and describes them as peaceful and not very technologically advanced. They're threatening because of the tech and instructions they're receiving from the "Future Guy".
Humans in the Mirror Universe (the Terran Empire). Instead of greeting the Vulcans peacefully, as per the "real" timeline, Mirror Zefram Cochrane (even without the evil goatee) attacked their ship and stole all the technology they could find, thereby starting the aggressive and militaristic Terran Empire on its course.
Humans are this, which is a major theme of the franchise.
Another example would be the Genii on Stargate Atlantis. Of course, the bar for entry to the cosmos is much lower in this franchise since the only requirement is often "figure out or obtain valid gate addresses."
Although it's less obvious, the Goa'uld are eventually shown to be this: the vast majority of Goa'uld seem to be Brilliant but Lazy or suffer from Creative Sterility, and they have salvaged and reverse engineered nearly all of their technology from other races. In any fair fight between humans and the Goa'uld, the Goa'uld lose; their weapons are almost entirely Awesome but Impractical. More than enough to intimidate Iron Age cultures, but when someone else has access to equivalent Phlebotinum from the Precursors or managed to engineer some of their own, the Goa'uld are in trouble. The Goa'uld actually recognize this, and so do their best to destroy potential competition before they can pose a real danger.
A Saturday Night Live skit from the '80s featured an Alien Invasion by a race that apparently hadn't advanced past muskets. When asked how they got the spaceship they came to Earth in, one scientist says, "Our guess is they stole it." The whole thing looks like an homage to The Road Not Taken.
A major plot point in several incarnations of The Hitchhiker's Guide to the Galaxy, when Ford and Arthur end up on a spaceship with the rejects from an allegedly-dying planet. Basically, the most intelligent caste tricked everyone else into evacuating their planet under the pretense that it was going to become unable to support life. They kept the manual labourers and workers, getting rid of only those who were culturally or industrially unproductive: bureaucrats, insurance salesmen, telephone sanitizers, hairdressers, advertising executives etc. These lesser castes eventually landed on prehistoric Earth, equipped with advanced technology but not knowing how to make or repair it themselves. It's suggested that these people were behind the legend of Atlantis, and eventually wiped themselves out in a spectacularly stupid manner. An aside/footnote in the novels (a Guide entry, in the TV series) explains that with this useless third of the population out of the way, the people of Golgafrincham made great cultural, scientific and technological advances before being wiped outby a virus contractedfrom a dirty telephone. In the novel in which they appeared, Life, the Universe, and Everything, Ford tells Arthur that these are the ancestors of modern humanity, not the Neanderthals Arthur tries to teach Scrabble to.
Humanity is one of the least-advanced major races, having only achieved interstellar capability after the Centauri made contact and opened up Earth to trade. The gap in technology contributed heavily to humanity's near-defeat in the Earth-Minbari War.note The Centauri warned against provoking the notoriously isolationist Minbari, which EarthGov took as an attempt by the Centauri to maintain a monopoly on Earth's interstellar trade. Things went downhill from there. At least partly in response, the humans have formed a corporation, InterPlanetary Expeditions, to perform archaeological surveys with the goal of locating and exploiting the technology of the First Ones. The main plot kicks off when an IPX survey locates Z'ha'dum and awakens the Shadows.
The Narns have reverse-engineered the technology of their former Centauri occupiers and use it not only to maintain their own empire but to sell to less-advanced races.
Even the Minbari - the most advanced of the younger races - are the beneficiaries of Vorlon technology they don't even fully understand themselves.
In Andromeda the Magog do not wear clothes or use weapons (although they do have language and fire) and their only battle tactic is the Zerg Rush, yet they have starships. It is later revealed that the Magog everyone is aware of are just shock troops used by their leaders who do indeed have a respectable level of technology/
The Kroot are an avian-descended race of barbaric cannibals, who were still using black powder weaponry when the technologically-advanced Tau found them. But, the Kroot still know how to build and fly their Warspheres, mainly because they happened to eat some Orks, among whom where some Ork Meks — Ork Meks have basic knowledge of engineering hard-wired into their DNA, while the Kroot have the ability to absorb useful traits from the prey they eat. It's heavily implied that the Kroot purposely keep almost all of their technology outside of travel low so that their race remains strong and their focus remains on gaining good genes from other organisms, rather than inventing stronger weapons.
The Jokaero are an inversion of the trope. The ape-like creatures are capable of building advanced technology up to and including spaceships, but no one's been able to quite determine whether they're actually intelligent, or if this is an instinctive ability. They behave almost like animals in spite of their advanced technology.
The humans in the setting count too. Their technology has regressed massively since they first colonized space, and even more since the Imperium was re-established. At this point they can reproduce an increasingly shrinking number of old designs, but they don't understand the underlying principles of their technology at all. Attempting to do so is both is one of the highest of heresies, and attracts the attention of demons.
The Vargr in Traveller. It's not so much that they are unadvanced as that they are so erratic that it is hard to imagine them actually having time to build starships before they are wrecked by the next civil war.
The Space sourcebook for GURPS 3rd edition had tables for randomly generating alien civilizations; a roll of 3 on 3d6 in the "Technology Level" table would result in this trope. (4th edition sadly removed the possibility.)
In the Phase World space opera setting for Rifts, the United Worlds Of Warlock was founded when a spacefaring Dwarven nation who used magic to make space travel possible with 19th century riveted-iron ships met a medieval Elven nation who didn't even know what outer space was and who'd colonised several worlds via magical gateways.
The adventure game Star Trek: Judgment Rites features an alien colony ship filled with seemingly retarded aliens (very humanoid ones, in best Star Trek tradition) who aren't even aware that they are on a ship at all. And the ship is about to land on top of a colonized planet. The mission actually ends up going in a completely different direction, when Kirk and his crew are transported into an alien dimension, but the origin and/or fate of the ship are never revealed.
The Doog in Star Control 3 show barely the intelligence to speak properly, and have probably received most if not all of their technology (whatever little they have) from their masters, the Ploxis.
The Rikti in City of Heroes are have energy weapons, teleportation, anti-gravity, Independence Day-style ships that are capable of traveling between Universes, and shapeshifting. All this without ever learning how to split the atom.
To be fair, they've had tech given to them back in the time of the Egyptians and killed all their gods, so they're certainly not incompetent, but have never developed a need to learn how to use what we would consider conventional tech. That's not to say they aren't advanced in their fields, they simply developed in what is a rather backwards fashion.
The Covenant from Halo. Their technology is far advanced of humans, but it's all copied from Forerunners, and upgrading the technology is considered heresy. In the books, the humans are able to upgrade the technology with relative ease, and it's also shown that Covenant mathematics is quite crappy compared to what humans know.
Ironically, other supplemental materials point out that the Prophets and Elites in the B.C. era were already at roughly the same technology level as 26th century humanity before they ever began reverse-engineering Forerunner technology.
The Jackals (or Kig-Yar), who are more like privateers than full members of the Covenant, have had space-faring technology before encountering the Covenant. In fact, it is a Jackal ship that makes first contact with a human vessel in the Halo: Contact Harvest novel before a Brute cruiser (with Tartarus on it) arrives to Harvest to lay waste to the planet.
The novel Halo: First Strike reveals that the Covenant have their own AIs, but these are seriously hampered by the same religious dogma as the rest of the Covenant. When Cortana begins messing around with the settings on the slipstream drive and the plasma weapons, increasing their effectiveness, the Covenant AI shows up, angry at this heresy. It even appears to just be a human AI with Covenant programming shoved into it.
The Rakata as seen in Knights of the Old Republic faced this problem at the end of their Empire. Their galaxy-spanning dominance was based on technology that relied as much on the Force as science to operate successfully and when they lost their natural Force sensitivity, the technology ceased to function.
In Command & Conquer 3: Tiberium Wars, the Scrin are implied to be less "insufficiently advanced" and more "insufficiently prepared" - the forces assigned to protecting their mining operation were intended for a planet where all native life was either extinct or on the verge of it. Instead, they were lured to Earth a century or two early, and ran headlong into two massive, technologically advanced, and unified global militaries, and despite being ill-equipped to face such a force, they are able to inflict massive damage on both GDI and Nod before being routed and driven off.
In Meteos, the inhabitants of Boggob are still in their Stone Age. They're able to hold up against the onslaught of Meteos impacts that have annhilated countless other civilizations, however, through Ewok-level craftiness. They actually discover space travel in this way.
The Ceph in Crysis are a play on this. The Ceph fought in the games are vulnerable to human weapons and can be contained by near-future human militaries despite predating humanity on Earth. It turns out, however, that this is because those Ceph are only just now waking up and are hurriedly adapting to human technology and numbers and adapting to Earth's environment. And by the third game, they're easily smashing CELL military resistance. But this pales in comparison to the true Ceph based in their home galaxy, who have had five hundred million years to develop, and are pretty much gods compared with humans and the Ceph on Earth.
An episode of Isometric features Dangerman fending off a comically inferior alien invasion. It is noted that these aliens do not natively understand the concept of detecting vibrational energy (what we call "sound"), have a visible spectrum that stops just short of "ultra-red" and "infra-violet" (Dangerman is perplexed by the "invisible assassin" and his bright glowing red "stealth" outfit), are apparently highly vulnerable to banana cream (said assassin's dying attack is to throw such a pie at Dangerman, to no effect), and lack the ability to jump (thus parking their craft six feet off the ground, allowing easy access). None of this seemed to be a problem before; they just picked the wrong planet to invade this time, is all.
Pretty much everyone in Spacetrawler, where the highly intelligent Eeb have been enslaved by the rest of the galaxy's intelligent species and put to work building all their advanced technology.
The opening quote is from a Halloween special of The Simpsons, where humans destroy all their weapons after achieving world peace and Earth is in turn invaded by Kang and a Kodos - armed with clubs and slings.
Kang: (pursued by Moe) Ah! He's got a board with a nail in it!
In another special, Kang and Kodos abduct Marge using a lasso rather than an abduction ray of some sort.
An episode of Duckman had Ajax abducted by "inferior beings" from the planet Betamax. They're dumb enough to consider Ajax's nonsensical ramblings to be wisdom of the highest order (though they have developed big screen televisions, because they have their priorities straight). When asked how they managed to acquire a spaceship, they claim it's a rental.