You can use it with the free flex sdk so you dont need Flash.
To use classes like the FileSystem stuff, you can use an AIR project.
fl.* and mx.* classes (such as UIScrollBar) are not included in the free flex sdk, however you can use them if you make your own swc file and include it in your project using a trial version of flash. (drag and drop the classes you want to the library window from the components window and click generate swc in the publish options)
I have to say, the amount of code it requires to create a simple button with text, or to create a textbox that scrolls is pretty nutty. Having to scatter your logic across async event handlers is a bit infuriating too.