What SuperF4 basically does, is kill the process of the foreground window when you press Ctrl+Alt+F4. You might think, doesn't Alt+F4 do this? Well, it's a bit different. When you press Alt+F4, the program can refuse to quit. Windows essentially only asks the program to quit, and lets it decide for itself what to do (almost always it behaves just as if you would have pressed the × in the upper-right corner)