John the Ripper is a fast password cracker, currently available for many
flavors of Unix (eleven are officially supported, not counting different
architectures), DOS, Win32, BeOS, and OpenVMS.  Its primary purpose is to
detect weak Unix passwords.  Besides several crypt(3) password hash types
most commonly found on various Unix flavors, supported out of the box are
Kerberos AFS and Windows NT/2000/XP/2003 LM hashes, plus several more with
contributed patches (over 40 of additional hash and cipher types).

WWW: http://www.openwall.com/john/