It's still at a pre-Alpha stage, but you can get regular updates from the lead developer at @BaptisteGelez (the account is on a Plume instance but it federates through #ActivityPub, so you can follow it on Mastodon etc).
There's a demo Plume instance at:
Developers can find out more here:
@switchingsocial ooh and it's Rust, not Ruby.
@switchingsocial looks really interesting. Activity pub is really in everything these days, isn’t it?
mastodon.at is a microblogging site that federates with most instances on the Fediverse.