It is a tiny application that lets you hide the window of the top most application when you click the hotkey. This means that if Notepad is the program that currently has the focus, hitting the hotkey will hide the Notepad window.
When the application is hidden, App Hide will add the name of the application to menu sitting on your tray icon. Right-click the little umbrella icon to see the list of hidden applications. Click on the application name to un-hide it.
The program is free and works well on Windows 7, Vista and XP. Download App Hide.