PeerTube seems fine for a YT alternative (only because it’s pretty much either it or Odysee, that’s what happens when you have an effective monopoly on user-generated content like YT does, and PeerTube IMO needs to take off sooner rather than later given how ridiculous YT’s censorship has gotten lately), and then of course Lemmy (this platform) is looking really good so far as a Reddit alternative and I’ve only been on it for a day now, ditto for Pixelfed as an Instagram alternative.

And then of course there’s Mastodon for a Twitter/Facebook alternative.

Also, Matrix seems fine for a Discord alternative, but moderation is all over the map.