what is Flex?

                 Flex applications are Rich Internet Applications that are built using tools from Adobe. These Flex applications run inside the Flash player, leveraging the existing installed base of the Flash player.

                Flex is made up largely of two parts. The first is an IDE built on the open source Eclipse platform. That tool is called Flex Builder.As well, an SDK will be made available to developers who want to build Flex applications. The SDK will include the Flex compiler, giving developers who code by hand (without the IDE) the ability to create Flex applications. The other part of Adobe Flex is Adobe Flex Enterprise Services.

Download Flex Builder 3 here