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.
I tested this MOD for a while.
It makes realy fun when you can play long parties about 10000+ rounds and even short battles.
You have evertime something to do and wehn not you make something wrong, it is never boring. The gameplay is great. It uses the strenghs of Civ IV and adds alot of new.
A bad thing by this mod is that it takes 3 minutes or more to start, but this is only a little thing. (by my first game it's also takes 15 minutes)
I wold say this is the best MOD for Civilization IV: Beyond the Sword