"Runs on Windows and Mac OSX Intel platforms."
If you only run on Windows or OS X, it's windowless, but it's not headless.
Headless means something running on a command-line console, and you can't run either of those operating systems that way.
If you only run on Windows or OS X, it's windowless, but it's not headless.
Headless means something running on a command-line console, and you can't run either of those operating systems that way.