Imperial Domination (series)!

0 A.D. is a free, open-source, cross-platform real-time strategy (RTS) game of ancient warfare. In short, it is a historically-based war/economy game that allows players to relive or rewrite the history of Western civilizations, focusing on the years between 500 B.C. and 500 A.D. The project is highly ambitious, involving state-of-the-art 3D graphics, detailed artwork, sound, and a flexible and powerful custom-built game engine.

The Battle for Wesnoth is a turn-based tactical strategy game with a high fantasy theme.

Set a generation before the events of the original Warcraft began, Warcraft II is a real-time strategy game by Blizzard Entertainment. Cunning, sinister, and seemingly unstoppable, the demonic Burning Legion prepare to launch their long-awaited assault on the mortal world. Survival is a matter of strategy, as the Reign of Chaos begins…

Freeciv is an open-source, turn-based strategy game based on Civilization II. Inspired by the history of human civilization, the game commences in prehistory and your mission is to lead your tribe from the stone age to the space age...

Widelands is a free, open source real-time strategy game with singleplayer campaigns and a multiplayer mode. The game was inspired by Settlers II™ (© Bluebyte) but has significantly more variety and depth to it. Still, it is easy to get started through playable tutorials.

FreeCol is a 4X video game, a clone of Sid Meier's Colonization. While remaining faithful to the original in terms of mechanics and gameplay, FreeCol sports a new set of redesigned graphics. Moreover, in addition to the classical Colonization rules, it features an additional ruleset that incorporates ideas that didn't make it to the final version of Meier's game, requests by fans and original concepts like new European players with new national bonuses.

C-evo is a freeware empire building game for Windows

Fulfill Your Quest For Global Domination

TripleA is a free (under GPL) turn based strategy game based on Axis & Allies board game. A wide variety of map scenarios have been developed for TripleA (World War II, Punic Wars, Napoleonic wars, etc.) with a variety of rules, units and many options (such as "low luck" which reduces the number of dice rolled making game depend more on strategy).

Advanced Strategic Command is a free, turn based strategy game. It is designed in the tradition of the Battle Isle series from Bluebyte. ASC can be played both against the AI and against other human players, using hotseat or PlayByMail. It is also used to run the multiplayer universe Project Battle Planets.

UniWar is a turn-based strategy game where players battle it out on the field with units of differents races, building bases and using the terrain to overcome their opponents towards victory. Several modes are available along with many maps to play.

Bos Wars (formerly known as Battle of Survival) is a futuristic real time strategy game (RTS). It is possible to play against human opponents over LAN, internet, or against the computer.