The PolarBear µblog server is where my main personal fediverse account is, I am @hamishtpb on there. Registrations are open but please read the rules and be aware that there is a federation limit & block list based on the principles therein.
IceShrimp is a micro-blogging server with mastodon compatibility and loads of nice features. It is ultimately based on the Misskey server project, another ActivityPub system. It is part of the Fediverse.