Ring is up to their second beta release but is now the first for being part of the GNU. Ring Beta 2 offers multi-device support and a decentralized username registry that's currently considered experimental. There is also support for Ring URIs as another decentralized way for sharing your contact information.
Ring is GPLv3-licensed, makes use of the OpenDHT protocol, supports end-to-end encryption, and more.
Those wanting to learn more about GNU Ring and its hopes, see this morning's release announcement and visit the official site at Ring.cx.