I'm currently working on an alternative to Medium. So far it has all the elementary things like a working editor, notes and highlights, a decent commenting system. There are publications too, with teams, submissions etc. User profiles and publications have custom domains, custom CSS for branding. There's also a somewhat half-working Github integration for advanced writers but I'll need to work on it a fair bit to polish the edges. At some point, I'd ideally want to open-source the editor/bloggy bit and have people self-host it and perhaps push their content back to the platform for centralized distribution if they want.

It's still a work in progress and I'm trying to figure out some sort of strategy, especially a content policy around not allowing clickbait and spammy "how to use learn redis in 3 minutes" type articles. I'd probably have to cap the max number of users and publication to a few thousand since I don't have the resources for this to be anything more than a hobby project.

I'm aware of a couple of others working in the same space. Write.as comes to mind, thought I don't think they're doing publications etc.