Opcrack is a password cracker based on rainbow tables, a method that makes it possible to speed up the cracking process by using the result of calculations done in advance and stored rainbow tables.
Ophcrack is being developed by Objectif Sécurité under the GPLv2 license.Details
A set of rainbow tables has been created and optimised for use with Ophcrack. Most of them are available for free. A more advanced set of a size of more than 2TB aimed at security professionals can be bought for $949.