As far as existing tech goes, I personally like and use Matrix.
Mastodon seems promising as a social media replacement, and PeerTube has the tech for YouTube replacements. Both of these two are using ActivityPub, which is on Wikipedia here: https://en.wikipedia.org/wiki/ActivityPub
The problem comes with content. Matrix is in the strongest position at the moment imho - moving chat platform has the least network effect, and it has the most effective (only?) bridges between "standard" centralized services out of the three. Mastodon has a decent presence, especially of tech people, but not so much outside of the tech or "got banned from twitter" bubbles. PeerTube is in the weakest position of the three afaict - it's mostly again the tech bubble and the "got banned from youtube bubble", but with a much worse distribution.
The tech on Matrix and Mastodon at least seems well established though[0], and I think both would succeed if not for the massive network effects of YouTube/Facebook/Twitter/etc.
My honest opinion is that even if a federated solution doesn't exist or isn't far enough along yet for any of the above it would be better to break down the current state of things and force the creation of one.
[0] I've not used Peertube really, so I don't know how far along it is.
