FlashDevelop is a development environment for Flash Actionscript 2 (AS2) and Actionscript 3 (AS3).
FlashDevelop supports jScript, HTML, XML y CSS.
FlashDevelop can have a complete development environment with all its features: search and replace, search files, debug, codes valid, etc. It also support many plugins, these make it more functional.
FlashDevelop is an open code aplication and it is free. It is possible the best application to program AS2. It is even superior to other commercial programs of the same type.