The University of Minnesota technical report describing XLISP-Stat is now available online in HTML or for download in PostScript. It introduces the features of XLISP-Stat and gives a fairly complete description of the differences from vanilla LISP. More info is at Luke Tierney's XLISP-Stat homepage. A better reference is Tierney's book, published by Wiley.
Forrest Young teaches a course in XLISP-Stat at UNC, for which HTML notes are available. These also describe the use and modification of his ViSta system, a visual statistics program based on XLISP-Stat.
You can down load the current version of my XLISP-Stat code for Generalized Estimating Equation models , model formulae , or Cox regression and play with it. Please tell me about any bugs.