SocialDocs: ActivityPub implementation notes + ecosystem links

Hi everyone,

I’ve been building Social Docs

https://socialdocs.org

a practical companion to the W3C ActivityPub/ActivityStreams specs, focused
on helping developers ship working federation. It includes protocol notes,
implementation guides, a reference section, and a few small tools
(validator, actor inspector, WebFinger lookup).

We already have a few collaborators. I'd like to add some of the things
we've learnt along the way. What would help most is links to ecosystem
projects or resources I’ve missed (servers, libraries, tooling, test
suites). Even one or two suggestions in reply would be great.

Best,
Melvin