Freeciv
Freeciv is a free and open source, multi-platform empire building strategy game inspired by the history of human civilization
Warzone 2100
Warzone 2100 is a free and open source, multi-platform multiplayer 3D real-time strategy game
LinCity-NG
LinCity-NG is a free and open source, multi-platform city simulation game and economic strategy, a polished and improved version of the classic LinCity game
UFO: Alien Invasion
UFO: Alien Invasion is a free and open source, multi-platform, real-time strategy and tactical role-playing game
C-Dogs SDL
C-Dogs SDL is a free and open source, multi-platform run-and-gun game in which players work together during missions and against each other in a “deathmatch” mode
Crispy Doom
Crispy Doom is a free and open source port of Doom with enhanced-resolution, limit-removing, based on Chocolate Doom
Tux Football
Tux Football is a free and open source, multiplatform 2D football game in an arcade style
Chromium B.S.U.
Chromium B.S.U. is a free and open source, space-scrolling shooter in an arcade style
Dungeon Crawl Stone Soup
Dungeon Crawl Stone Soup is a free and open source game in the Roguelike genre, an adventure through dungeons filled with dangerous monsters in search of the mysteriously fabulous Orb of Zot
Scorched3D
Scorched3D is a free and open source, multi-platform simple turn-based artillery strategy game in real time