Caveman2Cosmos is a CivFanatics community mod that add new features and content to the Civilization 4 experience, with almost daily updates since November 2010. It is the spiritual successor the The Civilization 4 mod Rise of Mankind and its addon A New Dawn, and combined the work of over 100+ modders to create a mod to "rule them all". It is developed by StrategyOnly Productions with its modding team made up of prominent members of CivFanatics.
A very good exteceve mod full of intence and exciteing chalanges never before seen in any other Civ Mod. Its still a bit buggy, but playable. But what do you expect from a mod created by a single, GENIOUS man. :D
Edit:
Ok, I completely change my mind. I have been playing it since June of last year and I'm STILL playing it. It may be buggy, but the loads of features and such makes up for it...