Eressea is an open-ended multi-player computer moderated fantasy turn-based strategy game world for any number of players.

It consists mainly of player-populated islands separated by oceans, and players control a growing number of units of a given race to build empires, armies and fleets.

Like most open-ended games, Eressea has no declared objective, it cannot be "won".

Playing is free, although signups for German players (who make up 80% of the population of Eressea) have now been tied to a donation for an animal conservation charity.

The game is internationalized with support for English- and German-language play.