The file extension AS identifies source code files in the scripting language ActionScript. It is a Macromedia (now Adobe) language developed for the control and generation of interactive Flash applications. Actionscript can also be used with the Adobe Flex and Air products, providing the ability to create rich Internet applications, desktop applications (via AIR), and apps for the iPhone, iPad, and Google Android.
The files are pure text files that can be opened and edited in any text editor. For the development environment Eclipse there is the ActionScript Development Tool (ASDT).