Normally, a widget cannot invoke a local executable, for some pretty obvious security reasons.

However, if you're willing to drop the security on your device, it can be done.

There are two ways - use the "exec://" protocol with an XML object:

var x:XML = new XML();
x.onData = function(data) {
     trace(data);
}
x.load("exec://mycommand");

...or use the "bactick" ASnative extension:

  import com.chumby.ChumbyNative;

  var data:String = ChumbyNative.backtick("mycommand");
  trace(data);

You should always use the first one if the command takes more that a few milliseconds to run.