Ophcrack offers one of the best free password recovery solutions in the market. Ophcrack comes in two versions: a stand alone installer and a Live CD. The stand alone installer requires you to additionally download separate rainbow tables whereas the Live CD already has them. As the stand alone installer uses about 1.5GB of rainbow tables, it offers much better recovery. However, the download size is certainly an issue. Also, the Live CD version is a bit easier to use for cracking passwords.
So, I will discuss only the Live CD version. You must choose the right version of Ophcrack Live CD for your operating system. If you use Windows XP, the download (Ophcrack XP Live CD) is nearly 415MB whereas for Windows 10, Windows 8, Windows 7, Windows Vista and Windows 2008, it (Ophcrack Vista Live CD) is about 495MB. Ophcrack may be identified as a virus by your anti-virus software. That is a false alert and should be reported to the antivirus company.
To crack passwords with Ophcrack, download the iso file for the appropriate Live CD and burn it on a compact disk using an image burning software. If you use Windows 7, you can use your OS's inbuilt image burning software.
Then boot the computer whose password you wish to recover using that disk. Ophcrack is fully automatic and you don't need to do anything from your side. It will automatically detect users and start the password recovery process. Then, it will display their passwords on the screen. You can note them for logging in to the locked account.
Ophcrack recovers passwords nearly 99 times out of 100. Ophcrack is limited to recovering passwords upto 14 characters.
Offline NT Password Recovery & Registry Editor
Another open source recovery software that resets forgotten Windows passwords. Offline NT Password Recovery is also needed to be installed on a CD before working. However, there is also a version that can be installed on USB drives to create a bootable usb drive (if your motherboard supports it). Its small size (nearly 3MB) makes it an excellent alternative to other bulky recovery options.
It just has one con. Its interface being completely text based is not for the lovers of GUI based systems. To reset your password, just boot into your computer using the Live CD or the USB drive and follow the on-screen instructions. Your password will be changed to a blank one. This software works on Windows 7, Windows XP, Windows NT and Windows Vista. It also supports 64 bit versions of these Operating systems.
Cain & Abel
Cain & Abel is another free password recovery software. Unlike the software mentioned above, Cain & Abel needs to be installed on another administrator account on the computer containing the locked account. It also requires separate downloading of rainbow tables. Since, you can use inbuilt Windows functions to reset a password if you have access to a working admin account on the computer, I see no use for this software unless you are desperate about recovering your password. Cain & Abel works only on Windows XP.