The Role-Playing Game game Mutant Chronicles (along with its tie-ins, collectible card game Doom Trooper, battle game War Zone and the 2008 feature film), although it takes place somewhere in the XXVIIIth century, is actually steampunk, as the Mutants and Dark Symmetry (a kind of evil power field) rendered all electronic devices unreliable and therefore practically unusable, so humanity was forced to rely on steam-powered ones. This was averted in later editions of War Zone, where the universe turned more to Diesel Punk and Cybertronic remained straight cyberpunk.
Warhammer's Dwarves and Chaos Dwarves have loads of steampunk contraptions, including a chopper and for one character, body armour which helps him move. The Empire also has a steam-powered tank.
Warhammer: Age of Sigmar continues the trend. The Kharadron Overlords, an entire faction of Sky Pirate dwarves with enormous fleets of Magitech dirigible skyships and entire flying cities, are some of the most Steampunk-stuffed creations you will ever find.
The Alchemical Exalted are heroes of a clockwork world who are implanted with steam (and other weird materials) powered devices that make them more effective as hero figures.
The D20 roleplaying game Etherscope is set in a Victorian, steampunk world complete with the usual paraphernalia. The main difference being the existence of the titular 'etherscope' which allows for the creation of computer-like mechanisms, amongst other things...
3.5 even features several Prestige Classes made for Gnomes which feature them as steampunk or Clockpunk mad scientists.
Eberron invokes this trope, along with Magitek, but is more magic-based technology than steampunk. Actual technology is rare and often not worth it, due to magic being so readily available and easy to learn.
Some of the more advanced realms in Ravenloft feature steampunk elements.
GURPS 3rd Edition had a Steampunk sourcebook, which included various steampunk devices, details of Victoriana, and contained three steampunk settings: Etheria (Planetary Romance); Iron ("conventional" dystopian steampunk) and Qabala (a weird variant, essentially "Golempunk"). This was followed by Steam-Tech, with further gadgets including an automaton detective (which was not intended to resemble Mr Holmes of Baker Street in any way). The 4th edition of the game has a developing line of PDF Steampunk sourcebooks which not only provide 4th edition game mechanics for material from the older books, but bring the game's treatment of the genre more into line with 21st century fashion-driven steampunk. In GURPS Tech Level terms, steampunk is often considered TL5+1, TL5+2, or TL6+1 — that is, as far advanced as TL6 or TL7, but different.
The Mage Knight "Black Powder Rebels" faction was highly steampunk, including steam golems and a steam tank.
A Polish RPG now released in English, Wolsung Steam Pulp Fantasy, is more Steam than Punk, and the authors themselves call it Victorian Fantasy. The setting is something similar to our world on the brink of the XXth century, but filtered through pulp fiction from the time, with a little bit of classic fantasy and lots of pop culture inspirations.
Airship Pirates is an RPG based on the songs of Abney Park (see Music), with all the steampunkery that implies — indeed, the world it describes is arguably even more steampunk than the songs, since the band describe themselves as "the only Airship Pirates" which the game understandably... changes.
Unhallowed Metropolis is set in the 22nd century, after a Zombie Apocalypse wiped out human civilization around 1900. Humanity has finally regained control of a few areas, and is going back to the last golden age of civilization, resulting in a "Neo-Victorian" culture with many elements of this.
The French Ecryme RPG is set in an alien world with strong Victorian-era aesthetics and classical steampunk technology.
Castle Falkenstein uses an essentially steampunk setting with added supernatural elements (including Engine Magick) for a good measure.
Deadlands is essentially steampunk of the Weird West variety. It handwaves typical technological limitation of steampunk technology by introduction of 'ghostrock', a kind of coal imbued with spiritual force that can give off tremendous amounts of energy and has other properties very useful to any Mad Scientist. Also, Manitous.
In Genius: The Transgression steampunk is the latest fashion fad among mad scientists. Humorously the actual Victorian mad scientists didn't create much in the steampunk style but many of them did use Baroque styles based on idealised 17th century fashions (which was also not actually used by 17th century mad scientists).
The FATE Jadepunk setting is Wuxia-toned steampunk that closely resembles the Asian-inspired Diesel Punk of The Legend of Korra, only minus the diesel. The book makes it clear several times that the core idea the writers worked to was to play up the 'punk' side and have the PC's go out to fight the corrupt authorities of Kausao City.
Tephra is a customizable steampunk RPG created by Cracked Monocle. Set in a unique world populated by elves, satyrs, and gnomes, it utilizes a single twelve-sided die.