@derickr I built it by hand by copying https://rknight.me/blog/building-an-activitypub-server/
It is relatively straightforward if all you want to to do is write content.
Happy to talk you through what I did.
@Edent I had found that link — but was hoping that the PHP world could coalesce around a single library, so that it would be an easy drop in for many many projects (including my own blogs etc).