The primary use of GNU social is to access the free network, be it ActivityWeb (ActivityPub) or Fediverse (OStatus).
Contrary to the original plan, we have merged The Free Network Module, WebFinger and LRDD into a single component named FreeNetwork. Likewise, ActivityPub and ActivityStreams 2.0 was kept the same plugin instead of separated.
The FreeNetwork component adds WebFinger (RFC7033) lookup and implements Link-based Resource Descriptor Discovery (LRDD) based on RFC6415, Web Host Metadata. It takes and produces both Extensible Resource Descriptor (XRD) and JSON (JavaSript Object Notation). Furthermore, and different from v2, every federation protocol will use the same distribution queue maintained by this component instead of holding its own.
We originally intended to have data modelling plugins that would extend the GS's "language". We then understood that it added more complexity than we wanted without any considerable advantage because we cannot dissociate data reception handling of the protocol itself.
ActivityPub already translates between activity and entity and allows plugins to extend it (thus serving a similar purpose to data modelling and representation plugins).
For remote ActivityPub mentions, ActivityPub handles it aided by the FreeNetwork component).
We still have to port OStatus (and ActivityStreams 1.0) and implement the distribution by FreeNetwork, although the base work is done. Regarding ActivityPub, although some of it already works, expanding the existing plugins to supplement ActivityPub, and full validation isn't ready yet. We will most likely finish the implementation of the whole federation stack in the next week.