Utopia [1] [2] by (back then) Mehul Patel's Swirve. Apparently it is still going on. Same with NationStates! [3] [4] Max Barry's book Jennifer Government is also decent.

[1] https://web.archive.org/web/20000816192919/http://games.swir...

[2] https://en.wikipedia.org/wiki/Utopia_(1998_video_game)

[3] https://en.wikipedia.org/wiki/NationStates

[4] https://web.archive.org/web/20021208105428if_/http://www.nat...