Alien Immortals or a Town that Traveled?
I've got two ideas, weigh in on which you'd rather play:
1. The players are powerful alien immortals marooned on Earth in the distant past. You're from a more advanced culture, and while you may look human, compared to the natives you're superhumanly strong and durable... and you age far more slowly. In this game the players will progress through historical eras, making the best of their situation or trying to advance humanity to the point where they can go home.
2. The players are the most capable residents of a small town that finds itself transported to another world. As such, it falls to them to explore this new world, protect their community from whatever threats arise, and deal with the natives... or they could abandon it and go off and have irresponsible adventures instead, what fun!
Either game will be run in a black box homebrew system. There are rules, but they're behind the scenes - you just tell me what you attempt, I tell you how it turns out.