ops5
OPS5 is a rule-based or production system computer language, notable as the first such language to be used in a successful expert system [...].

sharplispers/ops5 (Public domain)

This repository contains a Common Lisp implementation of OPS5. It was obtained from the CMU AI Archive on January 16, 2020, and modified by Zachary Beane to build and run on modern (as of 2020) Common Lisp implementations.

AI

Knowledge Representation Systems