This is a list of top 5 rules engine which can be used in your Java application. Out of below 5 frameworks, Drools is the most popular one.
|A Business Rules Management System (BRMS) solution which provides a core business rules engine (BRE), a web authoring and rules management application (Drools Workbench) and an Eclipse IDE plugin for core development
|A general purpose business rules and decision management system
|EasyRules provides the Rule abstraction to create rules with conditions and actions, and the RulesEngine API that runs through a set of rules to evaluate conditions and execute actions.
|A Clips-like Rule engine accessible from Java with the full power of Common Lisp
|A small, light and fast rule engine and scripting environment written entirely in Java; Gives access to all Java APIs