The Battle for Wesnoth - The Battle for Wesnoth is a turn-based tactical strategy game with a high fantasy theme.
TripleA - TripleA is a free (under GPL) turn based strategy game based on Axis & Allies board game.
Advanced Strategic Command - Advanced Strategic Command is a free, turn based strategy game.
ThumbZilla - Awesome thumb stomping and kicking action game.
Tanks of Freedom - Classic turn-based strategy game with two armies fighting against each other.
Warlight - Warzone is a customizable Risk-like strategy game where you compete with your friends to conquer the world.