FLEX is a programming language for building Rich Internet Applications (RIAs). It allows developers to create Flash applications using code rather than solely through Flash's interface. FLEX integrates with .NET by allowing .NET classes to be exposed and invoked from FLEX applications using technologies like WebORB and remote objects. The document demonstrates how to develop a .NET class, deploy it, create a FLEX application configured to call the .NET class, and run the integrated FLEX/NET application. IBM and SAP endorse FLEX for building visually simple and interactive interfaces that improve the user experience.