GroupKit is a Tcl/Tk library that makes it easy to prototype and build real-time collaborative applications (groupware), such as multi-user drawing tools, text editors, meeting tools, and much more.
Framework for software component integration, interoperability and adoptability through a XML based vocabulary: Software Component Integration Mark-up Language (SCIML)
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.