The CLiX project is a document transformation system which reads an XML file and allows the definition of transformation patterns to steer the transformation process.
This software was developed as part of a University project way back. However, recently I was reminded of it since it quite nicely demonstrates the use of the CLOS metaopbject protocol (MOP) to implement predicate dispatching for generic functions in Common Lisp. Especially this part may be of interest to others.