Eoops (Emacs OOP System) implements a Smalltalk-80-like language in GNU Emacs-Lisp
(Lewis 90). Eoops is a simple but efficient compiler for a class-based, single inheritance,
object-oriented language that uses explicit message passing for both method ...
Probably should mention this is from 1992 and doesn’t use CLOS. Is Eoops used in Emacs at all these days? Looks defunct: https://www.emacswiki.org/emacs/EmacsObjectOrientedProgrammingSystem