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 ⧉ – A general social network with no character limits, sort of like Facebook used to be on its older interface
Funkwhale ⧉ – Music and podcast storage and sharing
Kbin ⧉ – Link aggregation and discussion, sort of like Reddit
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 – All WordPress blogs can optionally be followed from Mastodon and the rest of the Fediverse
WriteFreely ⧉ – Minimalist blog where focus is on the text, like a calmer version of Medium
…and that’s just some of them! If you’re a techy person, you can see more comprehensive lists of server types at FediDB ⧉ and delightful fediverse apps ⧉.