Thanks for your interest in Copycat! Copycat is written in Common Lisp. The system is unfortunately rather outdated: it will not run as is without some updates for modern versions of Common Lisp, and some platform-specific modifications to the graphics files. I am hoping that it will be rewritten in a more platform independent way sometime soon. I am still making the source files available.
Here the Copycat Common Lisp source files.
Here is Jim Marshall's Metacat projectScott Bolland of the University of Queensland wrote a Java version of Copycat.