Warhammer40000 began as WarhammerIN SPACE! but is now pretty much its own entity; it still, however, has goblins in space, orcs in space, elves in space, ogres in space, the Church Militant in space, vikings in space, communists in space and Chaos Gods in space. Previous versions also had dwarfs in space.
Mage The Ascension was originally conceived as the medieval RPG, Ars Magica, IN THE MODERN DAY! — but then begat not only Mage: The Sorcerer's Crusade (MtAIN THE RENAISSANCE!), but, once White Wolf sold the rights to Ars Magica itself, Dark Ages: Mage.
Exalted, in turn, was supposed to be the original Old World Of DarknessIN PREHISTORY! — but now there's Scion, self-described as Exalted: IN THE MODERN WORLD WITH ANCIENT MYTHS ON TOP! (Though Scion doesn't necessarily match that description.)
Less problematical are the other historical games set in the Old World Of Darkness: Vampire: THE DARK AGES!, Vampire: THE VICTORIAN AGE!, Werewolf: THE WILD WEST!, et al.
There are also the settings in different cultures. Best known is the Year of the Lotus event which gave Asian treatments of every gameline, the flagship title being Kindred of the East.
Cthulhu Tech is Call of CthulhuIN THE FUTURE! Although not IN SPACE! as the Migou tend to blow up anything the NEG tries to keep up.
Steve Jackson Games has already done GURPS: Cthulhupunk, a sourcebook that puts Cthulhu IN CYBERPUNK!
Star Munchkin: "Kill the monsters. Grab the treasure. Stab your buddy IN SPACE!" [1]◊
It should go without saying that the other Munchkins are merely Munckin WITH PIRATES, WITH KUNG FU, IN THE WORLD OF DARKNESS, WITH ZOMBIES, and so forth.
The old Renegade Legions games is about The Roman Empire... IN SPAAAAAAAAACE!!
TravellerIntersteller Wars is the Greco-Persian wars in space, all the way from Marathon through Alexander's conquest.
Monopoly. Dear LORD, Monopoly. There's Monoopoly WITH SPONGEBOB! Monopoly WITH DISNEY!! Monopoly WITH LORD OF THE RINGS!! Just check Google Images. Or any store that sells classic games.
