Writefreely is listed as implementing ActivityPub based on go-fed. It relies on forks found in the writeas GitHub group:
It also relies on a small piece of code from the writeas web-core repository found in the activitypub directory to decode public keys and another from the impart repository to set the type of an http response. The activitystreams directory in web-core complements the streams directory with manually crafted types (not generated using astools, which did not exist in this form at the time the repository was forked).
The go-fed integration contains a set of handlers that are hooked directly to routes. The do not follow the development pattern suggested in the go-fed documentation because most of what it refers to did not exist at the time it was implemented in writefeely.
Although it is an interesting read, it does not help someone trying to figure out the best practices to integration go-fed in an application.