Glest

From the official website: Glest is a free 3D real-time strategy game, where you control the armies of two different factions: Tech, which is mainly composed of warriors and mechanical devices, and Magic, that prefers mages and summoned creatures in the battlefield. Glest is not just a game, but also an engine to make strategy games, based on XML and a set of tools. A few mods already exist. Release of version 1.0.0. was announced Sep 22nd 2004. Current version is 3.2.2.