Okay, sure, you could make an ultra-niche Fediverse app that has integration with a digital toothbrush or something, I’ll give you that. If three people can productively use it I’m not sure that counts as a form of social media, though. I’d use a descriptor more like “add-on service”. The “social” part means you need a certain number of bodies involved.
What’s the deal with Bonfire? As far as I can tell it’s microblogging with an emphasis on customisability.
Open source endpoints are great. I’m a big fan.
Edit: Oh hey! They have a blog post about that. So basically, it’s another framework on top of ActivityPub. I like the sound of that. From their GitHub they currently integrate microblogging and some weird thing that I can only describe as socially distributed accounting.