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.
MegaGlest is an entertaining free (freeware and free software) and open source cross-platform 3D real-time strategy (RTS) game, where you control the armies of one of seven different factions: Tech, Magic, Egypt, Indians, Norsemen, Persian or Romans. The game is setup in one of 17 naturally looking settings, which -like the unit models- are crafted with great appreciation for detail. A lot of additional game data can be downloaded from within the game at no cost.