- ap5 - A mature, embedded, in-memory Relational ObjectStore and a high-level/declarative/specification language
- DAYDREAMER - A goal-based agent that models daydreaming, emotions, planning, and serendipity
- Epilog System and Episodic Logic - In contrast to Epilog Inference Package, the original Epilog system was created by Schubert, Hwang and Schaeffer for knowledge representation in Natural Language Processing, and is documented at the University of Rochester's Web
- GBBopen - GBBopen is a high-performance open source distributed systems framework based on the concepts that were explored and refined in the UMass Generic Blackboard system (see PDF article on that history) and the commercial GBB product
- KR - Knowledge Representation is a highly flexible and dynamic prototype-based object system for Common Lisp
- LISA - Lisp Intelligent Software Agents - is a production rule system for Common Lisp
- 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 [...].
- PowerLoom - A (not written in Common Lisp) Knowledge Representation & Reasoning System
- RACER - RACER (Renamed Abox and Concept Expression Reasoner) implements a highly optimized tableau calculus for the description logic SRIQ(D)
- Scone - Scone is a high-performance, open-source knowledge-base (KB) system intended for use as a component in many different software applications
- SNePS - SNePS (Semantic Network Processing System) is an AI system for building, using and retrieving information from propositional semantic networks
Knowledge Representation Systems
Knowledge Representation Systems are an important subcategory of AI.