Peek Through is described as 'application for Windows XP, Vista and 7 which makes the foreground window transparent with the press of Hot Keys. You may adjust the amount of transparency and the Hot Keys'. There are three alternatives to Peek Through for Windows. The best alternative is Vitrite, which is both free and Open Source. Other great apps like Peek Through are Glass2k (Free) and Feewhee (Free).
About Vitrite Screenshot Vitrite is a small Windows utility that allows you to manually adjust the level of transparency for almost any visible window. It does this by utilizing a capability present in Windows for variable window transparency.
Small little program that allows Windows 2000/XP users to make any window transparent. Right-click on any window or press the keyboard shortcuts (Control + Shift + [0-9]) to make any window transparent. Its that simple.