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 looks really interesting. Activity pub is really in everything these days, isn’t it?
mastodon.at is open to all users and federates with most instances.
🇩🇪 🇦🇹 🇨🇭 mastodon.at ist offen für alle User und ist mit vielen anderen Instanzen verbunden.