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.
Everyday Software for the Researcher of Restricted Means: This project is intended to offer scientists and students with small budgets advanced versions of aqua-built desktop-editing, graphics and statistical applications for MacOSX.
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.
"Draft" provides a collaborative design environment to assist in prototyping projects - software or other - in a graphical manner. It's written in Java and provides an interactive, animated UI framework to create rich content. Emphasis is on ease of use.
CAVOR is an engine for building apps that involve both graphic and text/numeric data. Primarily GIS is the initial focus, but consider also CAD, CASE, project management (eg PERT charts), and others. Built-in scripting, C API, also supports Tcl and Java.