@AndreasDavour @amoroso @lisp this was done for the Expert System shell Babylon from GMD in Germany. It provided a flexible Frame system, which was built on top of Flavors. There were several Flavor implementations, besides the original one from the Lisp Machine. This MCS is one.

(Flavors was one of the first OOP extensions for Lisp. Classes and message sending. The idea of Mixins came from there. A later version of Flavors was one of the inspirations for CLOS.)