What FlashDevelop is...
It is an IDE that has templates for Flex 4, Adobe Air, and ActionScript projects. FlashDevelop is open source, but currently is for Microsoft Windows only. They are not against branching it out to other operating systems, but will have some work to convert 3rd party utilities to do it.
Some excerpts from their website (FlashDevelop homepage).
FlashDevelop is a free and open source code editor for every Flash developer.
FlashDevelop offers first class support for ActionScript (2 & 3) and Haxe development. Great completion & code generation, projects compilation & debugging, plenty of project templates, SWF/SWC exploration etc. FlashDevelop is also a great web developer IDE with source-control support (svn, git, mercurial), tasks/todo, snippets, XML/HTML completion and zen-coding for HTML.
Downloading and Installing.
- Start by downloading the latest version from the FlashDevelop website (Download FlashDevelop). Click on the latest release thread and scroll down to the download link.
- Run the installer. During the component selection screen, remove the Install Flex SDK option. We will be using the latest Apache Flex SDK.
Configuring for Apache Flex SDK
- Start by select Tools-->Program Settings...
- On the left hand side click on "AS3Context". Scroll down on the right to "Default Flash Version" and set the default to at least a minimum of 11.1.
- Click on the "Installed Flex SDKs". Click on the "..." button to the right of it. This will popup a window to manage the SDKs available to the IDE.
- Click on the "Add" button. This will add an empty template for the SDK. Click on the path to the right and click on the "..." button to locate the SDK folder. Once you've located the sdk, it should load in the rest of the information. Click the ok button to close out the popup.