And by that I mean,
An http server that serves word-like rich formatted text documents and includes a web-based rich formatting text editor to write and edit these documents.
With some searching I found these might be candidates
Ghost
WriteFreely / Write.as
Plume
And maybe the following editors in some kind of standalone mode
TipTap
Editor.js
Quill.js
CKEditor 5
Slate.js
As far as the editor, this is great. I pasted formatted text out of libre office into it and everything was fine except the images. Way better than a lot of the options here.
Althought one caveat, and it might be a big one,
It seems it can’t actually host files publicly, you need to publish them to a third party cloud hosting platform…
But other wise, it’s very nice…
There has to be a way !
Look into the GitHub integration. Your pipeline could be StackEdit -> GitHub + GitHub Actions -> Self-hosted final destination.