Well, the best open source editor for ActionScript projects seems to be FlashDevelop , which is reviewed here... http://www.flashmagazine.com/1243.htm

These tools allow you to compile a SWF using ActionScript and no FLA. You have to dynamically attach all of your Flash Components programmaticall y via class-based programming, rather than via a "pretty" graphical interface.

If you are familiar with Java programming...