So for OStatus, you gotta implement:
* Atom (RFC4287)
* WebFinger (RFC7033)
* ActivityStreams (http://activitystrea.ms/specs/atom/1.0/)
* Salmon (http://www.salmon-protocol.org/salmon-protocol-summary)
* Portable Contacts (https://tools.ietf.org/html/draft-smarr-vcarddav-portable-contacts-00)
* PubSubHubbub (http://pubsubhubbub.github.io/PubSubHubbub/pubsubhubbub-core-0.4.html)
And this is the glue: https://www.w3.org/community/ostatus/wiki/images/9/93/OStatus_1.0_Draft_2.pdf