The Fediverse is quite varied, and often the platforms don't all talk to each other well/at all because they're doing different things.
To explain in relation to the alternatives to big media:
Twitter-like - microblogging and following users/hashtags: Mastodon, Misskey etc, Pleroma, etc, etc
Reddit-like - threaded conversation and content aggregation, following communities: Lemmy, mbin (kbin died), PieFed
Youtube-like - video content: PeerTube (or Loops for Tiktok-style short videos)
Instagram-like - sharing photos: Pixelfed
Facebook-like - social media: Friendica (also Diaspora which is like Google+)
Goodreads-like - tracking read books and sharing reviews: Bookwyrm
And more: Funkwhale, Hubzilla, Jitsi, WriteFreely, etc