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.
What can i say about this mod? it is utterly incredible: MASSIVE Tech Tree, LOADS of Units, this is the definitive Civ4 Experience, go from a Prehistoric Tribe to a true Spacefaring Civilization, this mod includes things like: Modular Structures, Orbital Infrastructure, things like Cannibalism, Human Sacrifice, and Slavery with Realistic benefits and drawbacks, it includes a very large selection of animals for hunting purposes as well, these animals can be hunted and captured to build a whole new slew of structures, Cities on Mountains are a thing as well, as are ground units crossing the Ocean through new improvements, this mod is highly customizable as well, and for an extra layer of strategy: try the Revolutions option set to on, it utterly changes the game as a new nation could literally pop up in your backyard.
Countless Features, MANY Units, Buildings and layers of depth, this is what Civ should be like, what are you waiting for? don't you have a Mod to download?
One thing though: This mod will cause Out of memory Crashes, but fear not for I have a method to solve this in the comments section (Don't lower the Mod's rating because of this: it is an issue with Civ4 itself, not the Mod)
anyhow: Download, and enjoy.