http://pump.io/ was one of the AP implementations suggested by @cwebber
I tried their remote registration with my social.coop id:
https://datamost.com/main/remote
got this:
> Error: social.coop does not implement registration_endpoint
...etc...
@bhaugen pump.io isn't speaking the activitypub api yet, but it's close to doing so
pump.io's "pump api" is what the activitypub api was derived from, but they aren't directly compatible
So.... soon, I hope!
More of the same (I think): https://social.coop/media/X-r1dqiUpQRpYfpW--E