A while ago I posted list of ideas for games I'll never get the chance to run. Here's some more entries from noisms' Gargantuan Tome of Unfulfilled Gaming Desires:
Catalogue 16a, book XVII, chapter 9, subsection IV, no. 163: A time-travelling game, probably using GURPS, in which a future civilisation creates time travel, goes back in time and contacts people from ancient Sumer, but is then destroyed by nuclear war. The player characters are ancient Sumerians who subsequently come across the gate that leads them to the future, which they travel through and discover a world without humans but all kinds of futuristic technology. And aliens. And radiation.
Catalogue 34j, book X, chapter 83, subsection I, no. 18: Warhammer Fantasy Roleplay 2e - Characters from the Old World travel off on a voyage of exploration and end up being shipwrecked and washed up in Cathay.
Catalogue 29a, book II, chapter 11, subsection X, no. 4: D&D Animal Fantasy a la Redwall, but rather than mice and otters and badgers and the like, the major races are all based on varieties of insects and spiders. Locust Bard, anybody? Tarantula Fighter? Wasp Mage? No takers?
Catalogue 2k, book LXV, chapter 1, subsection XX, no. 38: A forge-style, indie, story-games.com, you-only-play-about-three-times-before-it-gets-samey-and-boring style game set in the Stalinist USSR. Basically a variant on wink-murder or the Prisoner's Dilemma, the characters pass notes to the DM every five minutes saying which other player they want to denounce to the KGB and have sent to the Gulag. But the denounced players can save themselves by correctly guessing which other player dobbed them in. Works better if you also have to drink a shot of vodka every time you get sent to the Gulag.
Catalogue 6w, book C, chapter 91, subsection V, no. 20: The PCs are Russian adventurer/explorers in the vein of Yermak Timofeyevich, participating in the conquest of Siberia. A bit like the Wild West (so I'd use the Deadlands rules), except with Tatar raids, crumbling remnants of the Mongol Empire, lots of snow, and China, rather than California, waiting on the other side.