The AT Protocol stands for "Authenticated Transfer Protocol". It's an open, decentralized network for building social applications collectively known as the ATmosphere.

It differs from ActivityPub in key aspects. ActivityPub plans to borrow some aspects of ATProto in terms of discoverability with Discovery Providers and account portability with LOLA.

Applications built on ATProto include:

• ATFile File hosting.
• ATProto Camp Digital badges.
• BLUECAST Real-time audio streaming & karaoke.
• Bluemotion Videos.
• Bluesky Microblogging.
• Frontpage Link aggregator.
• Linkat "Link in bio" pages.
• Picosky Public chat.
• Smoke Signal Events and RSVPs.
• soleia Crowdfunding (in development).
• WhiteWind Blogging.

Some tools:

• Sky Follower Bridge Find your 𝕏 contacts on Bluesky.
• The Fediverse Report Keep up with federated protocols news.
• Bluesky Community Showcase