There are a lot of alternatives popping up: BlueSky, Mastodon, Farcaster, nostr. There are also some older protocols that people are still building on like secure scuttlebutt.

I've written about some of the differences of these protocols here:

https://mirror.xyz/mattdesl.eth/_F9vQAUeeBB9AJNwMNaE_G5kTcl1...