The Tholos project aims to create an open,  distributed platform for 3D worlds.

What distinguises Tholos from many other shared vitrual world systems
Most shared virtual world systems have a setup whereby a user connects to a server with a fat client. The world contents are either already on the user’s machine or are downloaded on demand from the server to the client.
Tholos is aiming for an agent-based thin client system. This has as a big drawback that all rendering is done server-side. What is sent from the server to the client is up to the agent, but will at first be opengl commands.

The first goal is to have a server that contains a universe and a html 5 webgl based client.