Rule Engines Overview

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Jess	Jess is a rule engine and scripting environment written entirely in Java by Ernest Friedman-Hill at Sandia National Laboratories in Livermore, CA. Using Jess, you can build Java software that has the capacity to "reason" using knowledge you supply in the form of declarative rules. Jess is small, light, and one of the fastest rule engines available. Its powerful scripting language gives you access to all of Java's APIs.
Drools	Drools is a business rule management system (BRMS) and an enhanced Rules Engine implementation, ReteOO, based on Charles Forgy's Rete algorithm tailored for the JVM. More importantly, Drools provides for Declarative Programming and is flexible enough to match the semantics of your problem domain with Domain Specific Languages, graphical editing tools, web based tools and developer productivity tools.
Jamocha	Jamocha is an open source rule engine. The objective of Jamocha is to provide a high quality rule engine and expert system shell environment. Furthermore, we would provide the required development tools and a best practice methodology for rule based applicaton development.
JRules	ILOG JRules is a complete Java business rule management system (BRMS). ILOG JRules gives you the power to control your business policy changes-with confidence and without compromise.
Blaze Advisor	Fair Isaac Blaze Advisor is the world's leading business rules management system, maximizing control over high volume operational decisions. Blaze Advisor provides companies across industries with a scalable solution that delivers unprecedented agility and actionability for smarter business decisions.
PegaRULES	Pegasystems' unique approach to rules management is based on the belief that, like business data, business rules should be managed as a separate corporate asset. The PegaRULES enterprise rules engine separates business logic from your mission-critical applications and enables your enterprise to capture, manage, and execute your business policies and practices.
Mandarax	The aim of the mandarax project is to integrate reasoning into Java. The original Mandarax is an API for managing derivation rules in Java, and a (Prologish) inference engine to execute rules.
OpenRules	OpenRules is a full-scale BRMS, Business Rules Management System. It provides a powerful while simple suite of open source components for Rules-based Application Development. Using familiar tools such as MS Excel, Google Spreadsheets, and Eclipse IDE, you may create complex decision support systems around an enterprise-class Business Rules Repository.
Zilonis	The objective of this project is to provide a Multithreaded Rules Engine platform and a scripting environment for Java based applications.
SweetRules	SweetRules is a uniquely powerful integrated set of tools for semantic web rules and ontologies, revolving around the RuleML (Rule Markup/Modeling Language) emerging standard for semantic web rules, and supporting also the closely related SWRL (Semantic Web Rule Language), along with the OWL standard for semantic web ontologies, which in turn use XML and, optionally, RDF. (SWRL rules are essentially an expressive subset of RuleML rules.)
Prova	Prova (from Prolog+Java) is a rule-based system for Java and agent scripting and information integration extending the Mandarax engine with a proper language syntax and enhanced semantics. It combines natural syntax and typing of Java with Prolog-style rules and database wrappers. Java calls may include both constructor and method calls as well as access to public variables in classes.
Hammurapi Rules	Hammurapi Rules is a rules engine for Java developers. In Hammurapi Rules rules are developed in Java language. It supports forward and backward reasoning.
Common Knowledge	Common Knowledge from Object Connections is the most comprehensive and versatile infrastructure available for the management and automation of business rules and application logic. Common Knowledge is the only combined business rules engine and visual studio environment that allows business logic to be represented in multiple intuitive formats, reflecting the way you run your organisation. Supported formats include decision trees, decision tables, decision grids, rete rules, workflows, flowcharts, state-maps and scripts.
Haley Business Rules Engine	The Haley Business Rules Engine (formerly known as HaleyRules) is the industry's fastest and most scalable business rules engine. It works with your organization's applications to quickly and consistently apply the business decision logic you've captured as business rules. Haley's business rules technology accelerates application development, simplifies application maintenance, and dramatically reduces the cycle times needed to make changes in business rules.
CLIPS	CLIPS is a productive development and delivery expert system tool which provides a complete environment for the construction of rule and/or object based expert systems. Created in 1985, CLIPS is now widely used throughout the government, industry, and academia.