Glest is a free 3D real time strategy game, available for several operating systems.
The core game allows the player to take control of two completely different factions: Tech, which is mainly composed of warriors and mechanical devices, and Magic, that prefers mages and summoned creatures in the battlefield.
Very cool and complete warcraft-like strategy game, pity there's no multiplayer yet.
Download GLEST here... http://www.glest.org/en/index.html