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
Those are the built in templates, what you add is your markdown for your post. You’re not actually adding that. It isn’t quite click to save, but it’s similar. Write freely may be the closest bet for free