REX is the application name given for Talon Computing Rule Engine Express. As the name suggests, REX is a lightweight rule engine that is used by your development team to process business rules and react to decisions arising from those business rules.
REX is a framework for describing business logic for various aspects of your application. It allows you to decouple business logic from your application logic and make it configurable by business analysts. REX provides you with a desktop application that enables you to develop, maintain and test business logic independently of your applications.