Realism: Invictus

Realism Invictus is a mod for Civilization IV with over 15 years of development.

Mod for Civilization 4: Beyond the Sword
Over 130 new techs across every era. All techs have voice acting.
21 new civics, 3 for each category. "Old" civics are also reworked, in many cases completely so.
Over 80 new conventional promotions, including new promotions exclusive to naval units; this doesn't cover the traditions and doctrines, providing another 60 unique advantages to your units.
Over 160 new leaders for playable civs (over 300 total, including releasable civs and scenario-only leaders), each with their own personality, city lists and more
7 new leader traits: Humanist, Political, Progressive, Seafarer, Administrator, Legislator, Conqueror and Agricultural, to make sure there are many unique combinations to try out. Every combination of positive traits has at least one playable leader with it.
8 new playable civs, fully fleshed out with tons of content available for them
Many new gameplay mechanics, such as epidemics, barbarians that can settle into new civilizations, unique civilization-specific terrain improvements
And a lot more