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
Well, that’s just a blog. WordPress comes to mind, though try not abusing it by installing too many plugins and transforming it to an abomination that takes 3 seconds to hack.
There are probably more modern alternatives, I personally wrote my own blog system that uses ActivityPub to synchronise with Lemmy and others.