OpenDungeons

OpenDungeons is an open source, real time strategy game sharing game elements with the Dungeon Keeper series and Evil Genius.
Players build an underground dungeon which is inhabited by creatures. Players fight each other for control of the underground by indirectly commanding their minions, directly casting spells in combat, and luring enemies into sinister traps.

OpenDungeons is actively developed by a small but dedicated community, feel free to drop by on their forum if you want to contribute.