LISPDEBUG features a GUI, form highlighting, conditional breakpoints, code stepper, watching of variables or expressions, profiling, support of multisource projects and so on. LISPDEBUG is succeeded by Jabberwocky, no new versions are planned.
Information about LISPDEBUG can be found here. The version of LISPDEBUG on this website is not the latest version (I can no longer maintain this page). For the latest version of LISPDEBUG, see the Jabberwocky home page - Jabberwocky includes LISPDEBUG.