A graphics toolkit from the University of Stuttgart which provides an object-based interface to the X11 window system, based on CLX and CLUE. It doesn't seem to be maintained, and has some stipulations in the license worth noting. XIT is available from the AI repository: http://www.cs.cmu.edu/afs/cs/project/ai-repository/ai/lang/lisp/gui/xit/

CMU AI Repository