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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.
https://www.w3.org/TR/2018/REC-activitypub-20180123/
why? 'there are a lot of benefits to both (making your website part of the decentralized social web'