FSCrack is a front end for John the Ripper (JtR) that provides a graphical user interface (GUI) for access to most of JtR’s functions.
JtR is described as follows (from http://www.openwall.com/john/): “John the Ripper is a fast password cracker, currently available for many flavors of Unix (11 are officially supported, not counting different architectures), DOS, Win32, [...]