The Croquet Project

The Croquet Project:
Croquet is…
…a new open source software platform for creating deeply collaborative
multi-user online applications. It features a network architecture that
supports communication, collaboration, resource sharing, and synchronous
computation among multiple users. Using Croquet, software developers can create
powerful and highly collaborative multi-user 2D and 3D applications and simulations.

interesting project… didn’t work out of the box for me yet.