Open Cobalt

continuation of the Croquet project (built on Squeak Smalltalk), or a higher layer?

Open Cobalt is a free and open source software platform for constructing, accessing, and sharing Virtual World both on local area networks or across the Internet, without any requirement for centralized servers. The technology makes it easy to create deeply collaborative and hyperlinked multi-user virtual workspaces, virtual exhibit spaces, and game-based learning and training environments that run on all major software operating systems. By using a peer-based (P2P) Messaging protocol to reduce reliance on server infrastructures for support of basic in world interactions across many participants, Open Cobalt makes it possible for people to hyperlink their virtual worlds via 3D portals to form a large distributed network of interconnected collaboration spaces. http://en.wikipedia.org/wiki/Open_Cobalt

• that's a modified version of David Reed's Tea Time peer-based Messaging protocol

2021: looks like it's been dead for years

http://www.opencobalt.net/

Supports VoIP, XMPP, VNC.