There are 2 repositories under activitypub-protocol topic.
API Platform ActivityPub Support
Activity Hub .net implementation.
alternative docs for ActivityStreams 2.0 vocabulary
ActivityPub model and APIs for Dart and Flutter.
A decentralized social dating platform, using ActivityPub, PHP 7.4 API and React JS for the frontend. The platform will be federated across many different servers (instances).
Documentation and proposals for Activity Pub implementations of federated communities
fediverse protocol: following
fork of https://puck.moe/git/kroeg/cellar