Like mastodon, but a different protocol. Started off as invite only.
They use DIDs as the user identities.
They aren’t decentralized per se (which is a matter of controversy), but offer what they call “credible exit”. This seems to be a way to say “another service provider could show up and offer a replacement service offering, while the interfaces and identities remain constant”. They bill this as treating themselves as a future adversary.
Because credible exit != decentralized.. there’s no expectation folks are going to be hosting their own infra. Data is already balooning, so it will have to be commercially viable (as I understand it).