See the description of it and its FTP site location.
Fred Gilham has provided an updated version of it which works in CMUCL described in this Usenet post and posted here.
Various small bits of information can be gleaned by searching comp.lang.lisp
XIT
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.