Empyrion is a free multiplayer Real Time Strategy game.

Empyrion is a free Internet multiplayer Real Time Strategy game for 8 players, with integrated map and empire editors. Develop your own technology trees, provide your own art, share your empires with friends. Flexible unit properties provide for multiple weapons per unit, animated turrets, and much more. This game is part of the Synthetic Reality "Arcadia" family of games. (http://www.synthetic-reality.com/arcadia.htm) Players add additional channels at will using the integrated MIX server. Arcadia itself provides all networking support, in addition to text chat, voice chat, web browsing, and a parallel existence park environment for serenity, duck-feeding, and paintball while you wait for other players to show up. Arcadia allows you to create a personal identity with which to expose your current emotional state, and maintain a diary of other players you have met in the game.