Eclipse AXDT!

FlashDevelop is a free and open source (MIT license) code editor for Actionscript (2 and 3), Flex (MXML) and HaXe.

Adobe Flash Builder 4 (formerly Adobe Flex Builder) software is designed to help software developers rapidly develop cross-platform rich Internet applications (RIAs) and content using the open source Flex framework. It includes support for intelligent coding, debugging, and visual design and features powerful testing tools that speed up development and lead to higher performing applications.

Build amazing Flash effects and host them on your website for free.

FDT is a powerful Flash/Flex development environment for ActionScript, MXML and haXe. FDT enhances your workflow while increasing your productivity.