https://en.m.wikipedia.org/wiki/Bluesky

Bluesky began in 2019 as a research initiative at Twitter, led by then-CEO Jack Dorsey, to explore decentralizing the platform.[19] In August 2021, Jay Graber was hired to lead the Bluesky project and development of what is now the AT Protocol, with initial funding provided by Twitter.[20] Jack Dorsey left Bluesky Social's board by May 2024.[21] After the acquisition of Twitter by Elon Musk in October 2022, Twitter severed all legal and financial ties with Bluesky Social, leading to the rapid development of the Bluesky social app and the AT Protocol as a minimum viable product.[22][23] Bluesky launched as an invite-only beta in February 2023. In February 2024, the social app opened registration to the public, having reached around 3 million users by that time.[24][25] It became publicly federated later that month, allowing for third-party services on the AT Protocol to operate with Bluesky data.[26][27]