After attracting 2 million users in its first year of operation, Bluesky has grown another 400 percent with some recent help from Brazil and Elon Musk. Are these monthly or daily users, or just account holders? Nobody knows! But it still has a way to go to match X’s estimated 250 million daily users and Threads’ 175 million monthly users.
It’s technically decentralized, but functionally this doesn’t mean anything (yet) except for them not having to care about moderation.
It seems part of it might be open source, like the AT protocol, but not sure about all of it.