TripleA - TripleA is a free (under GPL) turn based strategy game based on Axis & Allies board game.
Age of Empires - Age of Empires is the critically acclaimed, award winning Real Time Strategy (RTS) game with a legacy spanning over 20 years and nearly a dozen titles in the franchise.
ThumbZilla - Awesome thumb stomping and kicking action game.
Stronghold - Stronghold Crusader is a RTS game from the series from Stronghold.
Warlight - Warzone is a customizable Risk-like strategy game where you compete with your friends to conquer the world.
ANNO - ANNO is a city-building and economic simulation video game series, with real-time strategy elements.