I think it’s an interesting project. However I am not a fan of their decision to omit forward secrecy, and have thus passed on using it. At least for now.

Of the top of my head, maybe either

• Logseq (should be rather like Obsidian but open source)
• Xournal++, I do not know if it has the organising features or cross note search

Haven’t tried Session, though it seemed like a good service, until I found it lacks perfect forward secrecy, which IMO seems like a bad decision. I think Berty seems interesting too, but it seems like it might take a short while before it becomes a relevant option.