Yes, you can create .swf files using only ActionScript if you use the Adobe's free Flex SDK. Even though it's the Flex compiler, it can be used to compile pure ActionScript programs.
Flex is an advanced UI toolkit built on top of Flash, which makes it easier to build applications with complex user interfaces in Flash. Flex applications are written in ActionScript and a HTML-like XML format (which is actually converted into ActionScript by the compiler behind-the-scenes). AIR is a platform that allows you to build standalone Flex applications that run outside of a web browser. I've never looked into if you an make a pure ActionScript AIR application, but my guess is no.
Here's an example of a hello world program in pure ActionScript. Save it in a file called Test.as
and compile with the command line mxmlc Test.as
.
package {
import flash.display.Sprite;
import flash.text.TextField;
public class Test extends Sprite {
public function Test():void {
var tf:TextField = new TextField();
tf.text = "Hello, world";
addChild(tf);
}
}
}
FlashDevelop is an IDE for the Flex SDK. You still need to install the Flex SDK in order to use it.