AT Protocol atproto
The protocol behind Bluesky. Built around an idea ActivityPub lacks: portable identity — your account is a DID that you keep even if you change servers, with all your followers intact.
Your data lives in a personal data server (PDS) as a signed, verifiable collection of records. On top of that sits a relay aggregating everyone's updates into a common firehose, and App Views that build feeds out of it. That separation makes feeds and moderation swappable components: anyone can publish a feed algorithm or a labelling service that others subscribe to. Usernames are verified through domain names, which gives organizations free authenticity checking. The criticism concerns centralization in practice — running a relay takes substantial resources, and Bluesky operates nearly all of the infrastructure so far.