Ghost-It! is a program that runs in the system tray, and lets you turn windows into ghost windows.
Ghost windows are very special windows. First of all, a ghost window is translucent, meaning you can see through it to whatever is underneath. Secondly, a ghost window will always appear on top of other windows. Thirdly, when a ghost window loses the input focus, it remains translucent and always on top, but all clicks will pass right through it like it wasn't even thereÂ—until it becomes the active window again.