In fossil's case, every instance includes those features, this makes the social platform "the web itself"

Having said that, there are central hosting projects, but where that has some value with git, git proper is distributed and does not need it but all the auxiliary stuff does. with fossil it provides almost no value. All the auxiliary stuff is built in so all it provides is a place to host. Which is fair but hosting is not hard with fossil.

https://chiselapp.com/

With everything included in fossil I abuse it as a personal social platform(think discord) super easy to host and it gets me chat, forums, wiki, and file storage. None of them great, but it is so easy I don't really care. voice and video do require an additional service, so there is that. Now I just need to find some friends...