A licensing note: the go-fed/activity libraries have been and still are Open-Source licensed (BSD). Proprietary Fediverse projects, like write.as, are free to continue using as much or as little of these libraries to build server applications from scratch. It is complex due to the sheer amount of customization.
However, as go-fed/apcore is a server framework and therefore much more of a plug-and-play, hand-holdy, almost-an-application kind of situation, I've licensed it as FLOSS under the AGPL-3.0 license