This program looks into the registry and displays product keys it finds there. It can find the Windows product key, the MS Office key, and many others.
It also has the ability to load a hive. (A hive is a binary file that Windows uses to store registry keys, as opposed to a text file such as a *.reg file containing registry keys in ASCII text.) This makes it great for a recovery situation. Imagine if your Windows broke. If the "load hive" feature got working in Wine, you could boot Linux off a thumb drive with Wine and use the Magical Jelly Bean Keyfinder to acquire your Windows key for re-installation of Windows (like if you lost the sticker, wanted to use the original OEM license, were given the computer without a sticker but it had Windows on it, etc).
Note: when you tell it to load a hive, it automatically appends system32\config\software to the path you give. So if you tell it to load ~\windows\system32\config, it will look for ~\windows\system32\config\system32\config\software (which doesn't exist, or at least shouldn't).