Flex is a highly productive, free, open source framework for building expressive web applications that deploy consistently on all major browsers, desktops, and operating systems by leveraging the Adobe® Flash® Player and Adobe AIR® runtimes.

Adobe® Flash® Builder™ 4 (formerly Adobe Flex® Builder™) software is designed to help software developers rapidly develop cross-platform rich Internet applications (RIAs) and content using the open source Flex framework. It includes support for intelligent coding, debugging, and visual design and features powerful testing tools that speed up development and lead to higher performing applications.