AutoHotkey Script that lets you toggle the topmost status of a window, or make it transparent.
By default the keys are set to Control+[ to toggle the "on top" status of a window, Control+9 to decrease transparency, and Control+0 to increase transparency of a window under the mouse cursor.
The keys are configurable via a "keys.ini" file that is created at launch, or can be adjusted by right-clicking on the taskbar tray icon and clicking on the options there.