Personal data storage can be decentralized, although that’s missing the social part of the social network.
Identities are set up through a centralized system that in theory they could change, but I wouldn’t bet on it.
Relays supposedly can be decentralized, but need to handle all data on the network. So they require massive hosting costs that keep going up as more people use bluesky. Only large corporations can likely afford to run them, and that hasn’t happened yet.
I don’t think there’s one that supports all of them yet. Probably the one that can handle the most is fedilab, which can handle mastodon and friendica, as well as a bunch of others like pixelfed, peertube, and pleroma. There’s also raccoon, which has separate apps for lemmy and friendica.