This is a cyber-security tool used for testing password strength. This tool can detect weak passwords which may pose a threat to any protected system. It was initially intended to be used in the UNIX environment, but it currently works in other types of systems like Windows, DOS, etc. This looks for encrypted logins, complex ciphers, etc. to look for vulnerabilities. 

Download link: https://github.com/openwall/john

This site is under maintenance,
some features might not work!!!