In fiction land, inventions are mind-bogglingly easy to make. This fellow is not a Bungling Inventor, The Professor or a Teen Genius. He might have a degree in Art History. However, he has managed to build some item of technology the entire industry could not replicate, probably in his garage using the knowledge he got from flipping burgers at McDonald's. Mostly he uses it for some mundane reason like fighting crime or making breakfast, or he just has it lying around so it can be given to the main character.
- Peter Parker invented a fluid that can be used as a stretchy rope and that hardens into a unbreakable barrier, in high school. There's been various explanations for this over the years. Some versions just have him as a budding super-genius on the same level as Tony Stark or Reed Richards, but some authors ignore this because it clashes with his "everyman" portrayal. One divisive explanation is that he gained instinctive knowledge of the composition of web fluid as part of his spider powers. Some continuities forgo this trope altogether and say that his father invented it.
- The original Superman claimed to have made his suit himself from a fabric he invented. You know, the suit that stays on him when he flies through the sun. Imagine the commercial and military applications for that.
- From time to time Superman's powers include super-intelligence. It's usually ignored because making him the most powerful and smartest person on Earth makes it really hard to write stories about him.
- In one episode of The Adventures of Superman ("Whatever Goes Up"), Jimmy Olsen invented an Anti-Gravity solution. In another, Perry White discovers a way to extract Uranium from seawater.
- In Ex Machina, Mitchell Hundred got a full blueprint for a jetpack from the aether in a dream, presumably as a side effect from his machine-talking powers. He also built a machine to nullify his own powers, some laser guns, taser gloves, a multi-sensor helmet, and maybe some other cool stuff we haven't seen yet. Justified, since his superpower involves communicating with technology.
- Tim Drake made himself a high speed skateboard after his dad sold his car, was the first Bat incorporate a separate computer in their costume instead of relying solely on the distant batcomputer, figured out how to run electricity through his cape to make it cling to whatever it was touching it and designed his Telescoping Staff to include an EMP emitter. While Tim is generally considered a Teen Genius he made several of these inventions in his bedroom at boarding school without attracting any attention.
- Norman the shopkeeper from the Brentford trilogy by Robert Rankin. His illuminated cowboy costume was less successful, as a static build-up caused it to collect sawdust and it (predictably) suffered a catastrophic short when someone tried washing it off with a soda siphon.
- Successful projects include a van fuelled by the driver's anger, and teleporting the Pyramid of Cheops into Brentford football ground. His inventions are invariable built from Meccano.
- The complicated robots Richard Wakefield makes should take more than his free time, but he is not a roboticist by trade.
- On The Big Bang Theory, when he lost his job, Sheldon, a theoretical physicist, somehow managed to genetically engineer glow-in-the-dark goldfish in under a month.
- Lampshaded and derided in an episode of Leverage. A CEO steals a valuable invention that an employee had created on his own over the course of years and years of working on it at home in every free moment he had. The Corrupt Corporate Executive mocks him that any claim he tries to make in a civil suit will sound like this trope (at least by the time the corporate lawyers are through with him).
- Destroy the Godmodder: The second game has the alchemiter, which allows the players to combine together various items to make new and cool exciting items, such as the obsidian tipped terror and ellorium autobow.
- In the first episode of The Flintstones, Barney invents a flying machine. In later episodes, Fred manages to create various concoctions out of his garage, including a shrinking potion and an invisibility formula... all this using Stone Age technology!
- Mr. Turner on The Fairly OddParents makes several homemade (and dangerous) items in his garage.
- Phineas and Ferb are pre-teen Summer Inventors.
- Wallace & Gromit: Downplayed with Wallace, as in the later installments he's explicitly using his inventions in several seemingly rather short-lived small businesses (that said inventions have a tendency to malfunction spectacularly might have something to do with this), but he doesn't seem to have very much formal training and the early shorts were rather vague about what he did for a living.
- A significant proportion of the code in most open source software is written by self-taught hobbyists working in their spare time. Considering that a lot of code needs basic math and that there are plenty of tutorials online, many of them for free, it's understandable.