Praedator - EnvyDeveloper
Not your typical expansion of Balmora - City of Balmora also adds 3 new factions with their own headquarters, several side quests and many caves to explore. You may even decide the future of Vvardenfell for decades ahead...
This mod adds a very large amount of content, so depending on how many mesh and texture replacers you use it may have a noticeable impact on performance in Balmora and the general vicinity. Using
OPENMW_PHYSICS_FPS may help.
City of Balmora.ESP