virtualworld

High Fidelity. The interesting part: 3D world with distributed network, low latency as a goal and voxel-based models and physics simulation. Good: Phillip Rosedale on board, who has already built a quite well-functioning 3D world with Second Life. Bad: Phillip Rosedale on board, who has already messed up the spread of a well-functioning 3D world with Second Life. Hmm. I think this is a case for "let's see".

Open Cobalt Website. What has become of OpenCroquet - apparently usable downloads are now available, not just an SDK. Peer2Peer virtual worlds in Smalltalk.