I’ve been using Obsidian lately. Proprietary with an open plugin ecosystem. Works well, makes it easy for me to integrate with other notes and such, but I haven’t figured out a good workflow for exporting work for submission. That said, it’s all markdown and there are lots of plugins for stuff like that, so it’s probably mostly just that I haven’t tried very hard.
In the past I’ve used Google Docs (proprietary), Scrivener (proprietary), Manuskript (open), Zim (open), and probably a few I’m forgetting. Really it just comes down to what you’re looking for out of the software, there are lots of options.
The biggest thing to keep in mind from a self-hosting perspective is local storage and easy backups under your own control. I use syncthing to keep my whole Obsidian vault synced across a few devices; for some software that’s easier or harder due to file formats and accessibility.