Ikariam!

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

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

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.

Crown of the Gods™ is a Free-to-Win MMO real time strategy game made by Gaming Addict Studios that is not, and never will be, pay to win. Crown of the Gods™ just finished its 3rd Closed Beta and will be going into Open Beta on January 23rd, 2016.

In the heart of the rainforest, a stunning view opens up to a white limestone city - your city in Tentlan. Travel back to mysterious cultures, become a mighty emperor, and experience the maya civilization in your own skin!

It is the year 2077, for the first time in its history mankind has finally began the colonization of another planet. Will the pioneers from Earth succeed in colonizing their new home or will they fail to survive against the harsh and inhospitable conditions of the Red planet?

Great Little War Game is a 3D turn based strategy game from Rubicon.

Here comes the Golden Age of Civilizations, a semi turn-based MMO strategy game, inspired by but not following the classic games of the genre, such as Age of Empires, Civilization and Rise of Nations; mixed up with MMO capability and flavored with the best parts of other good online games.