Revamp is mainly adding cut/planned content from original CoC, as well as adding some new characters.
Xianxia is based off of an older version of Revamp, and is missing some of its changes, but has more of a focus on adding Chinese/Eastern content, as well as a job system and reworked spell systems.
UEE is another branch of Revamp I believe, though I have no real idea since I haven't played it.