[ohtwenty]

Halcyon and Pinafore are both just front-ends for existing mastodon accounts (like brutaldon).

Pleroma is a different technology, but federates the same. As is Misskey; depending on what you're looking for in features either of those might do it more for you (or the glitchsoc fork of mastodon). (and theming is a thing, of course, regardless)

It's been posted here before, but http://fediverse.party/ is a nice little overview of the federated social web (over ActivityPub, I believe); https://the-federation.info/ is broader. Both have some small issues but are nice starting places.