Moom relies on something called the Accessibility system to do what it does. The good news is that OS X includes Accessibility support automatically in standard windows. That is, if the developer uses OS X’s built-in tools to work with windows, Accessibility support is a free add-on—the developer doesn’t need to do any extra work to support Moom.
But some applications use custom window code—for various reasons, they choose to create the windows and buttons on their own. In those cases, Accessibility support must be added by hand.