Movim is a federated Discord alternative, though not part of the fediverse/Activitypub, as it is based on XMPP instead. It’s still a bit clunky in the UX department, but is currently the most full featured federated alternative.

Also @HubertManne@piefed.social

CoMaps (which uses openstreetmaps) has the option of adding a link to a menu for restaurants, though I don’t think it has reviews.

I believe Flohmarkt is a fediverse alternative.

XMPP is an established federated messaging app with encryption.