Camera Mouse 2013 does that on windows for free. Not a great option since it doesn't always follow whatever it is tracking that well. You would need to go with

Camera Mouse 2013 does that on windows for free. Not a great option since it doesn't always follow whatever it is tracking that well. You would need to go with an expensive option like http://www.tobii.com/ http://www.tobii.com/ if you wanted good eye tracking, but that is expensive and I don't think Mac compatible. Plus, not always as accurate or easy to use as you would think.