Flex 2 has two sections in its product line, Flex Framework, and Flex J2EE enterprise server.

Flex builder is the kit to create MXML files, some like dreamweaver for html. Flex creates flash files with MXML component-based script, together with ActionScript classes, and ActionScript code embedded inside MXML. The difference between Flex and Flash professional is that Flex do simple jobs in graphics user interface, with Macromedia style components. The Flex J2EE enterpise server is another side of Flex, I think Flash professional could use it as well.

Some points of Flex J2EE enterprise server:

1. Support multi-clients synchronize. 2. JMS API(Java message I/O) support. 3. Flash clients could subscribe data objects on server, that server will push updates when happens. 4. Support session waiting if connection broken.