ASDF System Connections
ASDF-System-Connections provides auto-loading of systems that only make sense when several other systems are loaded. If I'm lucky, the examples on the project home page will make this clear!

ASDF-install package (obsolete) http://common-lisp.net/project/cl-containers/asdf-system-connections/asdf-system-connections_latest.tar.gz

This development tool is another one of Gary King's projects.