

Git exposes a lot of internals through odd commands, so I suspect you could manage synchronization by sending changes over email or something.
Bonus fun fact: there’s a git bundle
command that “dumps” the repository into a single file, that can be interacted with as a remote. So if you’re ever working with a local repository and want to put it on a server over ssh or something like that, you can just create a bundle, scp it over, and clone from that on the server.
I got the impression that the PolyMC situation was quite different, with that developer masking it and doing a minority of the work, but after one change made by the rest of the developers they snapped, used their control over the repository to remove the rest of the maintainers and take sole control over the repository.
I was aware of some shenanigans and hostility from PolyMC and never used it, but I got the impression there were no major outward signs before that happened?