It was once a commercial software development environment aimed at the 1980s AI market, and it contained many influential ideas. Notecards, for example, was a conceptual predecessor of Apple’s Hypercard, and D-EDIT and S-EDIT are sort of the canonical ancestral structure editors. Masterscope and the “file package” included system-management tools that combined features of version control and build systems, with comprehensive cross referencing support.
Medley was the latest release of the Xerox Lisp environment, before the whole environment was renamed Medley. It was originally written in Interlisp (a dialect separate from the MACLISP/Common Lisp tradition, with its own ancestry), but later, Common Lisp also became part of the environment. Medley includes WYSIWYG text editor (TEdit), email organizer (Lafite), performance tools (Spy) and many other libraries and user contributed code (from the 1980s).
The 1992 ACM Software System Award, to Daniel G. Bobrow, Richard R. Burton, L. Peter Deutsch, Ronald M. Kaplan, Larry Masinter, Warren Teitelman
for their pioneering work in programming environments that integrated source-language debuggers, fully compatible integrated interpreter/compiler, automatic change management, structure-based editing, logging facilities, interactive graphics, and analysis/profiling tools in the Interlisp system.
At this point the base system is usable enough on 64-bit OSes and quite fast (A $40 pi runs Lisp id sbout 150 times faster than a $30,000 Xerox 1108 in 1982).