BRL-CAD is a powerful cross-platform constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing for rendering & geometric analyses, network distributed framebuffer support, image & signal-processing tools.
Powerful platform for creating networked multiplayer 3D games. The system includes specifications for a client engine and 2 protocols. Demo apps: mud/moo proxy, tetris. Currently uses OpenGL, VRML, java, tcl. Client/server architecture for security.