We're building a new multiplayer IDE but for docs/tasks [1]. Local-first, real-time collaborative and end-to-end-encrypted sync. Not open source but self-hostable with a single binary and hackable with plugins (custom properties, views, code, etc).
I use Zim wiki for everything just now and I don't like it. I'm in the market for a replacement, and would even pay like with how Immich does it.
Unless the source code is available or you put it into legal escrow for when you go bust/abandon the software†, I will not invest my time and data into a system where I am entirely dependent on another organisation or service.
† And you will go bust or abandon the software before I die!
[1] https://thymer.com