This library was built to support the very little functions that pherephone requires. It might never be feature-complete but it's a very good point to start your activityPub journey. Take a look at activityserve-example for a simple main file that uses activityserve to post a "Hello, world" message.
For now it supports following and unfollowing users, accepting follows, announcing (boosting) other posts and this is pretty much it.
The library is still a moving target and the api is not guaranteed to be stable.
You can override the auto-accept upon follow by setting the actor.OnFollow to a custom function.