ActivityPub used by Friendica
ActivityPub is an open, decentralized social networking protocol based on Pump.io's ActivityPump protocol. It provides a client/server API for creating, updating, and deleting content, as well as a federated server-to-server API for delivering notifications and content.Notable implementations
Federated (server-to-server) protocol
Friendica, social networking software; implemented ActivityPub in version 2019.01.
Kbin, a news aggregator and discussion forum similar to Reddit and Lemmy.
Lemmy, software for running Reddit-style news aggregators and discussion forums. Any instance can use ActivityPub to interact with other forums and form a federated social network.
Libervia (in beta as of 2022)
Mastodon, social networking software; implemented ActivityPub in version 1.6 and released in September 2017. It is intended that ActivityPub offers more security for private messages than the previous OStatus protocol.
Micro.blog, a microblogging social network, added support for ActivityPub in 2018 and was enabled by default for new users in October 2022.
Nextcloud, a federated file-hosting service.
PeerTube, a federated video-streaming service.
Pixelfed, a federated image-sharing service resembling Instagram.
Pleroma, a lightweight fediverse server implementing ActivityPub since its first release.
WordPress via a plug-in to post blogs from users
WriteFreely, an open source and hosted blogging platform.