How to pin a window on top Mac

Does anyone know a way to keep window on top in OSX? I've tried Afloat and works with about 15% of the apps out there. I know that you can snap windows to different corners but I often need to be able to keep one window [IM for instance] atop of another. I can't believe there isn't "pin window" functionality in OSX, natively or third-party. Thanks!