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Related or similar projects
Thousand Parsecs is a FOSS project under development for creating Master of Orion-styled turn-based strategy/4X galactic conquest games. It has several front-ends including an OGRE-based 3D client.
Glest is a relatively mature FOSS real-time strategy game as well as an engine to make RTS games.
The Battle forWesnoth is another mature FOSS game, but aims not to be an engine but a single complete fantasy turn-based strategy game in the style of the Warlords titles.