Are there any good multi-player games that allows for optional long term collaboration?

I was thinking about setting up a game server for some friends and I, but I want it to be a game where you don't have to wait for others to be online to have fun.

I also want it to be a long-term thing, and where those who don't want to invest too much time can engage in casual play.

Bonus points if the game doesn't become cluttered with builds from players who drop out - I'd love to make it public (or close to it) and see what the world ends up looking like.

I was considering an open Minecraft server with some mods, but it's a bit too heavy once the amount of players becomes significant. Plus then I'd have to deal with griefers.

Oh, and of course, a game that does not break everything once it updates.