From Adobe Systems:
Welcome to the Adobe Flash Builder 4 (formerly Flex Builder) public beta release on Adobe Labs. The first thing that you've already noticed is that we are renaming Flex Builder to Flash Builder. This name change will create a clear distinction between the free open-source Flex framework and the commercial IDE. Flash Builder 4 delivers a long list of new features, plus improvements to many existing features.There are three main themes to this release: developer productivity, designer-developer workflow, and data-centric application development.