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 features of ATProto in terms of discoverability with Discovery Providers and account portability with LOLA.

Applications built on ATProto include:

• ATFile File hosting.
• AzSky Long-form discussions.
• ATProto Camp Digital badges.
• Blue Place Collaborative canvas.
• BLUECAST Real-time audio streaming & karaoke.
• Bluemotion Videos.
• Bluesky Microblogging.
• Bookhive Book management and reviews.
• Frontpage Link aggregator.
• Linkat "Link in bio" pages.
• pastesphere Text and code snippet sharing.
• Picosky Public chat.
• Pinksea Oekaki (computer doodle) image board.
• Recipe Exchange Recipes.
• Skylights Book reviews.
• skywatched Movie reviews.
• Smoke Signal Events and RSVPs.
• soleia Crowdfunding (in development).
• teal.fm Music tracking (coming soon).
• 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
• Bluesky Directory Find starter packs and lists.