How many types are there and how prevalent are they? I read some websites about "host your own server" and some were talking explicitly about Mastodon and some

How many types are there and how prevalent are they? I read some websites about "host your own server" and some were talking explicitly about Mastodon and some were like "let's do selfhostes microblogging with this AP server" And I asked myself, if I could use AP servers to follow people and let them follow me when they're on a public Mastodon instance.