Flex is a free, open source framework for building highly interactive, expressive web applications that deploy consistently on all major browsers, desktops and operating systems. It provides a modern, standards-based language and programming model that supports common design patterns. MXML, a declarative XML-based language, is used to describe UI layout and behaviors, and ActionScript 3, a powerful OO programming language is used to create client logic. Flex also includes a rich component library with over 100 proven, extensible UI components for creating RIAs, as well as an interactive Flex application debugger.