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.

"GNU FreeDink is a humourous 2D adventure/action game. It's a portable and improved version of the Dink Smallwood game which was released as Free Software by its author Seth A. Robinson. FreeDink can run the original game as well as its extensions called Dink Modules or D-Mods for short. FreeDink also comes with a game editor called FreeDinkedit, so you can create your own world! ..."

Avaneya is a science fiction FOSS game exclusively for the GNU/Linux platform. It focuses on social justice, human rights,city building, adventure, strategy, economics and sustainability amidst a Martian planetary setting in the future.

Scorched 3D is a modernization of the classic DOS game Scorched Earth. It's a simple turn-based artillery game and a real-time strategy game in which players can counter each other's weapons with creative accessories, shields, and tactics.

Rarely do major game developers and publishers make a cross-platform game, and those that do rarely release the game for all platforms at the same time. Usually if there is a Linux or Mac version of a game, it won’t be released for weeks, months, or even years after the Windows version.

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.

A cute, fun and free game. The latest release was in February 2009. Graphics have been improved. Characters added and few extra tracks. Check out the game.

Welcome to a Free Gamer special! People often accuse the Free software and open source game sphere of lacking depth, that there are few good games. In 2009 Free Gamer is dedicated to dispelling this myth.

Great free FPS game. It has in game level editor. Single player and multiplayer game play is available. Nice action and graphics.