http://www.indiedb.com/games/theworld < basic overview
http://www.iridiumbased.com/ < website for development
Sets up a game world that is similar to "The World" from the .hack// anime series. If you haven't seen it you should. Mind you it is fairly slow the whole way through but the plot is great enough as it is.
Anyways the game is the same general layout as the anime with some added areas and stuff that the "users" want to see of course. Have not played it yet so I cant give personal preference on game play.
Free to use on Friday and Saturday every week. Also it is $40 minimum to buy into early access Alpha right now for "unlimited time".