RTS Factions ("Nations") Multiverse RP
I think it might be fun to have an RP where the different factions from real-time strategy video games find themselves forced to interact. So you might get the Soviets from Red Alert fighting off the Zerg from Starcraft, who in turn are beseiged by the Aeon Illuminate from Supreme Commander. But all three are threatened by an alliance between the Americans from Warfront and the Marines from Natural Selection II.
Basically, through some method or another - perhaps a chronosphere accident, or a spell gone horribly awry - your faction finds itself on a [popular map from some game or another; or perhaps an entire planet]. After setting up the basic tools of survival, eventually they make contact with others. Fun ensues.
And then maybe throw in a few random events to shake things up - perhaps a meteor hurtling toward the planet, or a biblical storm, or a particularly great mining expedition, or even some cosmic accident transports the factions to [a new map from a different game with different resources] - possibly placing two bases in the middle of each other.
Any takers? Questions? Comments? Suggestions?