Ad Infinitum - Massively multiplayer game. [Open Source]
Building Virtual Worlds To Teach Archaeology: - Discusses the creation of a virtual world to teach archaeology and the life of the ancient Maya to a target audience of middle school students.
Fate - Massively multiplayer space trading and combat game. [Open Source]
Mars Simulation Project - Open source Java project to create a simulation of future human settlement on the planet Mars. [Open Source, GPL]
The Millport project - Development site for a massive multiplayer game with a graphical interface, written in Java. [Open Source, GPL]
The MUGU Project - Massively-multiplayer roleplaying game system, emphasising graphics over text. [Open source, GPL]
Oneiro - A text-centric, adventure game engine written in Java. [Open Source, GPL]
Tag3D - Interactive Virtual World system using Java3D and RMI. [Open Source]
Virtual Universe - More than only a simple 3d-chat: here a complete virtual reality is simulated.
Worlds.com - Chat in a virtual reality 3D world.