FlashDevelop is a free and open source (MIT license) source code editor.
FlashDevelop offers first class support for Flash ActionScript (2 and 3), Haxe and Loom development: great and fast code completion & code generation, projects compilation & Flash debugging, plenty of project templates, SWF/SWC exploration, etc.
FlashDevelop is more generally a great web developer IDE with integrated source-control support (svn, git, mercurial), tasks/todo, snippets, XML/HTML/CSS completion and built-in zen-coding for HTML.
These details are provided for information only. No information here is legal advice and should not be used as such.