Currently (2006-10), it requires Lispworks, an earlier version ran under Allegro. Some screenshots and details can be found among the Lisp(works) success stories.
SigLab
SigLab is a block-diagram programming system for signal processing. It was presented at the European Common Lisp Meeting, April 2006. The source code was
recently made available by its author, David McClain. As of 2012-04-27, it is no longer there.