AFAIK, ZeroSync is the name of the codebase the Devs are currently working on to get towards OneSync.

Quote from one of them in the Discord:

‘you have to go past 0 to get to 1’

They’ve also posted on their Twitter that prototyping of ZeroSync should start soon. So, If I would have to guess I would say ZeroSync will be tested and stuff and then the code will be polished up and released as OneSync (could be wrong).

Tweet: x.com