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 ...
It is. You can still use it. There is an implementation that byte compiles with just some minor warnings but EIEIO (a simplified CLOS version) is what is available in Emacs as built-in and there is much more available resources to learn from if you want to use an object-oriented system in Emacs.