Four free product key search programs

1 Product Key Finder
The original unnamed product key search engine is a pretty good keyword search program.
After implementing the Product Key Finder, a simple window opens showing your Windows product key along with the other product keys and the serial number that the Product Key Finder can locate.
Find keys for operating systems: Windows 7, Windows Vista, Windows Server 2008 and 2003, Windows XP, Windows 2000, Windows 98 and Windows NT.
Find locks for other software: Most Microsoft office 2016 product key and Adobe applications, more than 200 applications under the Product Key Finder site.
Unfortunately, Product Key Finder did not find the key in Windows 8 or Windows 10.
2 ProduKey
ProduKey is a completely free and easy to use lock search tool.
What I like most about ProduKey is the easy way to perform advanced search tasks such as downloading product keys from remote registries.
Find keys for operating systems: Windows 10, Windows 8, Windows 7 professional product key, Windows Vista, Windows XP, and Windows 2000.
Find keys for other software: Microsoft Office 2013, Office 2010, Office 2007, Office 2003, Exchange Server and SQL Server.
Everything works fine for me with ProduKey when I use it in Windows 10 and Windows 8.
3 Windows Product Key Finder Pro
Windows Key Finder Pro's Gear Box is another great utility that can find your Windows product key. It can also find product keys for some Microsoft Office programs.
Advantages include a very small download size, the ability to run it from a flash drive or other portable device, no compressed files to extract, and nothing to run to display the keys. Windows Product Key Finder Pro instantly displays product keys and allows you to save or print them for safekeeping.
Find keys for operating systems: Windows 7, Windows Vista, Windows Server 2003, Windows XP, and Windows 2000.
Find keys for other software: Microsoft Office 2013, Office 2010, Office 2007, Office 2003, and Office XP.
Note: Do not let the name fool you. The "Pro" in Windows Product Key Finder Pro does not mean it costs - it's really free to use.
It is said that both Windows 10 and Windows 8 are supported, but I could not find the product key when I tested v2.5.
4 WinGuggle
WinGuggle is a very simple key search program. WinGuggle easily finds product keys for popular Microsoft Windows operating systems and some Microsoft Office programs.
The main advantages include fast download size, no installation, access to some advanced tools and a very simple interface. WinGuggle instantly displays your Windows and Office product keys.
Find keys for operating systems: Windows 7, Windows Vista, and Windows XP.
Find keys for other software: Microsoft Office 2010, Office 2007, Office 2003, and Office XP.
Although WinGuggle supports Windows 8, Windows 10 and MS Office 2013, unfortunately, I did not find the correct key when I tried it.