Flash MiniBuilder is a lightweight IDE created for developing programs written in ActionScript 3. Flash MiniBuilder is itself written in ActionScript. MiniBuilder will become a strong IDE, both online and desktop, and will promote using ActionScript in unexpected places like on server-side, native desktop applications, embedded devices, etc. Also, other ActionScript projects can use the code completion engine in their own solutions.
This and other of it's unique features and concepts will make it the IDE of choice for a lot of AS3 developers.
MiniBuilder will benefit from Adobe AIR's ability to launch applications from the browser. Code samples, online tutorials, code libraries will be able to provide a direct launch link for their projects: "launch this project in MiniBuilder"