KlayGE is an open source, cross-platform game engine with plugin-based architecture. It provides a framework to make game development, testing, porting as simple as possible.
GMUVE (Graphical Multiuser Virtual Environment) is an engine/framework that lets large numbers of users interact in a 3D world. GMUVE is a peer to peer networked OpenGL application that can be used for MMPOG or 3D chat. It is available in Python and JAVA
Slut is a programming framework for generative, synthetic, interactive, network-enabled graphics. THIS IS AN OLD PROJECT. But since you are interested in it you should check out the SceneExpression project: http://labs.nortd.com/sx/