Magical Jelly Bean Keyfinder is a freeware utility for recovering the product key (cd key) used to install Windows from your system registry.
It has a configuration file that is updated by the community and retrieves product keys for many other applications. Another feature of the application is the ability to recover product keys from old Windows installations that are not running.
Works for installations Windows 2000, XP, Vista, Windows 7, 8 or 10. According to the manufacturer, the free version of Magical Jelly Bean Keyfinder can recover keys from 300+ different programs.
The "pro" version of the application (called Recover Keys) is not free, but may retrieve activation codes for 10,004 applications.