C-evo is another open source Civilization clone which I very much enjoy, due to the emphasis on strong AI and completely deterministic combat. This year has brought a a new release after a 5 year hiatus: http://civilization.wikia.com/wiki/C-evo
Nice, I didn't know a new version had come out. This game was written in Delphi, and open sourced a few years back. It has an API for writing computer controlled players, and a tournament mode for seeing which one comes out on top. That was where I learned function pointers, good times!
