Eressea
Eressea is a turn-based strategy game in a fantasy setting. It is an open-ended game, adding new players to the fringes of the world all the time. The game is free of charge, has around 1700 players and is growing rapidly even after more than six years.
The original game was written for a German speaking audience, and there is plenty of German material available on the web. Since early 2002 they are accepting English-speaking players as well, after having done a massive amount of localization.