From NTWind Software:
This program lets you close all running applications with just a single click. It doesn't use system resources because it only flashes a 'close' signal to all open applications on the desktop and then ceases. Just create a shortcut to the tool in the Start Menu, Quick Launch, Windows 7 Taskbar or elsewhere. You can always add a hotkey to this shortcut. It is really very handy if you are running ~20 applications and want them all to quit instantly. It works just as if you were pressing the close button for each application. Close All Windows is a very simple utility that doesn't require installation. No settings are stored in the Windows Registry or file system.