Stumbled onto this self-hosted outliner. Probably will never use it myself, but thought I'd share:

https://github.com/WuTheFWasThat/vimflowy

Demo: https://vimflowy.netlify.com

Here is another one: https://gitlab.com/NickBusey/BulletNotes

demo: https://bulletnotes.io/

Interestingly, this one also has Trello like features...

Hackflowy: https://github.com/abhshkdz/HackFlowy

Demo: https://abhishekdas.com/HackFlowy/