AFAIK, obisidian is:

• Not open source, treedome is open source.
• Uses a centralized server to sync your notes, treedome instead uses a single local file which you can sync, move around, however you want.
• Uses graph, treedome is working with trees and tagging instead.
• Uses plugins to add more feature to the notes, treedome doesn’t plan to do this. We at least want a complete experience out of the box, with notes files that’s fairly stable within a major version. I have to make it stable since the start because I’m already using it for work and personal.