ActivityPub is a W3C Proposed Recommendation as of 5 December, 2017:
“The ActivityPub protocol is a decentralized social networking protocol based upon the ActivityStreams 2.0 data format. It provides a client to server API for creating, updating and deleting content, as well as a federated server to server API for delivering notifications and content.” – W3C
ActivityPub is already implemented in the popular federated microblogging platform Mastodon.
As of the time of this writing, Mastodon alone had over 1M active accounts spread across 1,000 active instances.
A major goal of our project is to raise the number of ActivityPub instances by at least an order of magnitude as Indienet apps are, by definition, instances of one.
In addition to the main ActivityPub specification, there are a number of related specifications that we must be aware of. Most importantly, ActivityPub is based on Activity Streams 2.0 and implemented in JSON-LD. The general Social Web Protocols editor’s draft is also a good overview of related technologies.
PDF versions of the specifications are linked to below. The canonical locations of the specs is the W3C.