Globulation 2 is a RTS game with an unusual gameplay design. The source and media are licensed under the GPL.[1][2] The latest release of the game is 0.9.4.1 released on March 25th, 2009. It is programmed in C++. It uses the SDL[3] and Boost[4] libraries.

Really nice 3D strategy game for Linux. It has great graphics and the gameplay is enjoyable. If you like strategy games then Glest is something you should definitely install on your Linux machine.

Unknown Horizons is a FREE and open-source, real-time 2D strategy game for Windows and Linux. The game emphasis on economy and city building:

Expand your small settlement to a strong and wealthy colony, collect taxes and supply your inhabitants with valuable goods. Increase your power with a well balanced economy and with strategic trade and diplomacy.

Warzone 2100 is a free, real-time strategy and real-time tactics hybrid computer game for Windows, Linux and Mac OSX which offers campaign, tutorial, multi-player and single-player skirmish game modes, unit designer, unit experience system, and everything you would expect from a modern RTS game.

Savage 2: A Tortured Soul is a fantasy / science fiction, real-time strategy, fps, rpg game is a sequel to to S2 Games’ Savage : Battle for Newerth. Both teams of human and beasts are pitted against each other in a gameplay where strategy, agility and alertness is needed. Activities such as kills, deaths, assists, building razes, damage and score points are tracked.

Glest is a very good real time strategy game. It is free and works on Linux!

Freeciv is a turn-based strategy game, with some real-time elements, in which each player is the leader of a civilization, fighting to obtain the ultimate goals of a nation: The extinction of all other nations, being the first nation to plant a colony in another star system, or survival to the end of the game.

0 A.D. (pronounced "zero ey-dee") 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.

This game has become very popular. It is a first person shooter game with elements of real time strategy. Free to download and open source.