(1) For the Chromium-based operating system, see 
ChromeOS Flex.
(2) A development system for Flash-based applications from Adobe.  Introduced in 2004 as a J2EE application, Flex compiles ActionScript programming code and XML-based user interface descriptions (MXML) into binary Flash files (.SWF files).  It also includes a variety of user interface functions for creating rich client applications.  See 
Adobe AIR, 
Flash, 
MXML and 
ActionScript.