Also, today we launched the Fedibird Relay Service with pub-relay 2.0, which allows Mastodon, Pleroma and Misskey to participate.
https://relay.fedibird.com/
pub-relay 2.0 is a fork and maintenance of the Mastodon relays that I have stopped developing, with code added to accommodate Pleroma and Misskey.
https://github.com/noellabo/pub-relay