https://hyperclast.com/

I built it because Notion is way too slow. I loved Obsidian, but I wanted it to be multi-player so my whole team could use it. It is fast, open, and self-hostable.

It meets all the criteria you listed except the mobile app. Mobile app will be out next week. I'd happy to build any other features you need. Just let me know at k@hyperclast.com :-)