[rapnie]

There is some (renewed) interest but in various niches..

https://linkedopenactors.org/

https://codeberg.org/openEngiadina/cpub (though parent project switched to XMPP)

https://github.com/andstatus/andstatus/issues/499 (though stalled)

[mro_name]

I suppose openengiadina backed down from the activitypub complexity and doc and namespace 404s in the standard.

Neither am I convinced whether activitypub takes itself seriously as they don't keep a validator up. Nor is there a reference implementation, is there?

[easrng]

The reference implementation is basically "Do Whatever Mastodon Does" unfortunately.