Eve Online

http://www.eve-online.com/

Quoting from the website:

EVE: The Second Genesis, is a massively multiplayer, online, persistent world game. perhaps even too real to be called a game, but definitely more fun than reality. Played on the net by nerds who can't get a date, it takes place in a world that is alive and kicking every day, every hour. Players are spaceship captains cruising around the universe, trading, fighting and communicating with other players.

Uses StacklessPython for game logic on both server and client.