The Battle for Wesnoth Free turn based fantasy strategy game.

Advanced Strategic Command Free futuristic turn based strategy game

FreeCiv Free Civilisation style turn based strategy game

Scorched 3D Free 3D turn based strategy like Worms

Crimson Fields Free turn based strategy game

Wormux Free Worms like strategy game with open source mascots

Pingus Free Lemmings like strategy game with penguins

UFO:Alien Invasion A free squad based tactical strategy game

Glest Free 3D realtime strategy game

Free Orion Free turn based galactic conquest game