FlashDevelop is a highly customizable lightweight script editor with extended support for class based languages.
Although the program is designed mostly for ActionScript, other languages can be implemented quite easily too.
FlashDevelop is also very quick and simple to setup and easy-to-use as an external editor for the Flash IDE or as a complete open source development environment.

Main Features:
· AS3 Project management with seamless and optimized Adobe Flex SDK integration
· AS2 Project management with seamless Swfmill and Mtasc integration (using a portable standalone command line tool)
· Advanced ActionScript 2 and ActionScript 3 completion & code exploration with automatic classpath detection (even without project)
· Smart contextual Actionscript code generators
· SWF and SWC classes and symbols exploration
· Test movie in Adobe Flash IDE and with clickable error results (Flash CS3)
· MTASC compilation/code checking with clickable error results
Other Features:
· Types Explorer
· Automatically cleans ASO files of modified AS2 classes
· Files explorer (can create Flash 8 Trust Files for you)
· Automatic JavaDoc creation from methods
· Smart Actionscript help websearch on F1
· Jump to class/member declaration on F4
· XML, HTML/PHP, JS, CSS code highlighting,
· Multibyte character encoding
· Program menu customization with XML files
· as2api GUI for documentation generation
· Snippets
· Lines bookmarks
· Code folding
· Zoom

Requirements:
· NET Framework 2.0

What's New in This Release:
· Find and replace regex engine fixed
· TraceManager now resist message flooding
· Start Menu group creation is now optional
· Script errors are now ignored by the browser control
· Completion now shows local "Class" vars after new keyword
· Option added to generarate code always with access modifiers
· Option added to disable haXe compiler based completion
· Option added to disable the find text updating on F3
· Other small completion and UI bug fixes