What defines “social media sites?” Fediverse is just stuff that implements the Activitypub protocol. Mastodon, Pleroma, Pixelfed, Friendica, Lemmy, Honk, Peertube, and everything else listed here: https://en.wikipedia.org/wiki/Fediverse Basically they are all different platforms (not sites) people can run using the random domain names that they do.

Yeah, hard to answer your question as it is a bit like “Do you know some good email sites?”

Anyways, for a list of different fediverse software see: https://www.fediverse.party/

I prefer Mastodon and there are countless servers out there andkst of them differ in rules and appearance