FlashDevelop: An Open-Source Editor Designed for AS2/AS3

FlashDevelop is a .NET open source script editor designed mostly for Actionscript 2/3 development. FlashDevelop can be used as an external editor for the Flash IDE or as a complete open source development environment.

FlashDevelop is a very nice option for those looking for a quality/free ActionScript editor.  Also, if you’re still writing in ActionScript 2.0 and looking to convert over to ActionScript 3.0, this is a great tool that’ll get you used to constructing and using classes.

Features to be expected of Flash Develop are:

FlashDevelop has a nice docking interface.
FlashDevelop has a nice docking interface.
FlashDevelop has built-in support for many workflows.
FlashDevelop has built-in support for many workflows.
The Outline panel gives you an overview of your code.
The Outline panel gives you an overview of your code.
FlashDevelop's code completion works with your and others classes.
FlashDevelop's code completion works with your and others classes.
The Tasks panel help you track your project state.
The Tasks panel help you track your project state.

Additional Resources: