FediDB lists 67 software projects in the Fediverse. Just scroll through it and try whatever suits you.

My personal favorites:

• PieFed (Threadiverse)
• PeerTube (Videos)
• Mastodon (Microblogging)
• Bookwyrm (Books)

And lately I scrolled a bit through Wafrn, it's a whole different vibe over there. I don't understand much, but that's what I love about it.

So far, I've tried and enjoyed:

• Mastodon, a twitter-like microblogging platform
• Peertube, a peer-to-peer youtube-like video posting and streaming platform
• Pixelfed, an instagram-like image sharing platform
• Matrix, a federated IRC-style chatroom protocol (not really fediverse/activitypub, but still interesting)
• Wafrn, a tumblr-like with support for Bluesky's AT protocol too!
• Misskey, a unqiue social platform with lots of features, very popular with the Japanese art crowd
• Mbin, another reddit-like with lots of interesting features and a nice interface.

And there are still plenty more that I haven't really tried yet! The fediverse is pretty huge!

As for recommending specific sites, that's a bit harder since it's healthy that not everybody is on the same server. So I would just recommend picking a reasonably popular server with open registration.

i like NeoDB, it's handy for me to log movies/books/shows/music in one place

https://fedi.tips/

Lemmyverse.net is a very useful site to find communities that may not have federated to your instance yet (at least 1 user on your instance must be subscribed to it for it to begin federating). Especially useful for smaller instances.

You mean other federated sites? Mastodon, Friendica, PeerTube, to name a few.