Project Balance is a defunct mod that was focused on overhauling the balance of the game. It did not aim to add any major amount of content, instead trying to improve the content that's already there.
Its main features were:
- Technology spread has been overhauled so that technology spreads in a more realistic fashion
- Most realms that survived historically will be considerably more likely to do so. Examples include the Ethiopians and the Pagans
- The big land grabbers in vanilla now act more historically
- Conflicts, like Iberia or Byzantium, are no longer resolved in decades
- Improved cultural and religious spread
- Improved cultural buildings
- Reworked de jure kingdoms
- Reworked de jure and demesne law. Dejure law is more difficult to increase, but you can specialise it more.