Ruby/Password is a set of useful methods for creating, verifying, and manipulating passwords. It includes an interface to CrackLib, a library commonly used for checking password strength. It is intended to be used by system administrators who need to write Ruby programs that prompt for, generate, verify, and encrypt passwords.
nessus-xmlrpc is a Ruby library for the Nessus XML-RPC interface. You can use it to start, stop, pause, and resume scans. It lets you watch progress and status of scans, download reports, etc. It comes with an example command line program that shows how easy it is to interact with the Nessus scanner.