Long time back Macromedia introduced Flash, the next generation Multimedia. Flash was all about timeline-based approach. Consider everything as an image put in a strip that you run through very very quickly to get some movie. People started to realize that Flash they can do some real cool stuff with and we started to see new way of web content coming up.
When people realized that Flash can be used to do much more than static web content. But, when developers open up the Flash player they froze to see the timeline view. We can just not see programming the timeline way – we are OO guys.
So, Adobe decided to provide a way that works for developers as well and up came out Flex. Flex framework is a code library of components that facilitate building applications which run on Flash Players. Adobe also wanted to make sure that the community can benefit from the framework so they open-sourced the framework. Adobe also provided with a tool the Flex Builder based on Eclipse framework that assists developers to make Flex applications. The Flex SDK (software development kit) has all i.e. Flex source code library, compiler which will let you develop applications in any IDE (even a Notepad) but requires more time and effort to setup. The trade-off for the costly Flex builder is productivity and I find that value for money. Adobe also offers free licenses for students.
Some thing about Flex applications… Flex applications are written in MXML which is a declarative language based on ActionScript 3. The MXML files are first compiled into an ActionScript3 file and then the same is compiled in a SWF file. the SWF file can then be executed in any Flash player.