0 A.D. is a free, open-source, cross-platform real-time strategy game.
0 A.D. (pronounced "zero ey-dee") is a cross-platform real-time strategy (RTS) game of ancient warfare. It's a historically-based war/economy game that allows players to relive or rewrite the history of ancient civilizations, each depicted at their peak of economic growth and military prowess.
Open source FPS/RTS Game
Unvanquished is a fast-paced, futuristic FPS with RTS elements, pitting technologically advanced humans against hordes of highly adaptable aliens. The player can choose from either team, providing a fresh gameplay experience on both sides of the conflict. The game is under highly active development, with a new alpha release being made at the beginning of each month.
The engine for the upcoming Open Terror. This engine is based mostly on the XreaL project, with parts taken from AltUrt and ioQuake3 too. Still under development, but will soon be one of the first modern semi-realistic open source FPS games.