Download of ophcrack 3.6 was on the developer's website when we last checked. We cannot confirm if there is a free download of this software available. This free software was originally created by Objectif Sécurité. The software is included in System Utilities.
From the developer:
Ophcrack is a free Windows password cracker based on rainbow tables. It is a very efficient implementation of rainbow tables done by the inventors of the method. It cracks LM and NTLM hashes and uses brute-force module for simple passwords. It features real-time graphs to analyze the passwords, audit mode, CSV export and much more.
You may want to check out more software, such as Speeditup Free, WinTools.net Professional or Advanced Registry Optimizer, which might be similar to ophcrack.