As well as Mastodon ⧉, there are lots of other server types on the Fediverse, for example:
BookWyrm ⧉ – A social reading platform, an alternative to Amazon’s GoodReads
Friendica ⧉ – Lots of add-ons like calendars and photo albums, but a bit more complicated to use because it provides loads of options. Allows long posts with no character limits.
Funkwhale ⧉ – Music and podcast storage and sharing
Mobilizon ⧉ – Event organisation, the Fedi’s alternative to Facebook Events
OwnCast ⧉ – Video livestreaming with a chat window at the side, very much in the style of Twitch
PeerTube ⧉ – YouTube-style video sharing site which uses P2P technology to allow even small servers to have videos go viral, as the more people view a video the more bandwidth it gets
PixelFed ⧉ – Photo sharing site, similar in style to Instagram and Tumblr
WordPress – Independently hosted WordPress blogs can be turned into Fediverse servers using a special plugin
WriteFreely ⧉ – Minimalist blog where focus is on the text, like a calmer version of Medium
…and that’s just some of them.