Some HN readers may be interested to know that Prism is written in Common Lisp. It is one of the largest and most featureful Lisp programs I know of.
For many years Prism was the sole planning system used at the University of Washington Medical Center. It is still used there for the cases that can't be handled by the commercial system they now have. It has also been used at some other medical centers, as a platform for research projects that require access to system internals -- which the commercial planning systems do not provide.
The project page is http://www.radonc.washington.edu/research/cancer-informatics...
According to that page, it is covered by the Lisp Lesser GNU Public License, LLGPL.