They open-sourced the front end for a specific build, which is still available. But you are correct- the backend and most recent frontend are not open source.

Obsidian has the lead on convenience with their $8/mo "Publish" environment.

Joplin has some self-hosted dockerized options I think.

I believe the devs of LogSeq intend to compete in this market- but Nostr needs a totally FOSS LogSeq that interopetates with Nostr natively. LogSeq is written mostly in Clojure, which I'm not sure is really a benefit in regards to Nostr applications. It needs to be rebuilt to serve us optimally here.