The makers of @pixelfed, the Fediverse photo sharing platform, have just created a slick new guide to the Fediverse at:
It's got a list of Fedi projects, a list of mobile apps for Fedi platforms and an opt-in directory of people to follow.
The directory is particularly interesting as it works very differently to FediFollows or Trunk. You add hashtags to your profile plus a special extra hashtag #Fedi22, then submit your profile to the site, and it will become searchable for the tags in your profile.
(And, yes, Mastodon is part of the Fediverse, see here for details: https://mstdn.social/@feditips/108215973331591896)