The virtualbox-COM Ruby gem is a library that provides a low level Ruby binding to the VirtualBox API, allowing anyone to control VirtualBox from Ruby code. It can create, destroy, start, stop, suspend, and resume virtual machines, and also list virtual machines, list hard drives, network devices, etc.
Binary Puzzle Solver in Ruby is an automated solver for Binary Puzzles (a kind of logic game) featured on http://www.binarypuzzle.com/. The solver contains an API and a commandline program and explains why it thinks the player should place a 0 or a 1 in the box. Although it contains only a subset of the moves the authors could think of and does not use backtracking, it was able to solve all the puzzles from binarypuzzle.com which the authors tried.
AffirmIt! is a supportive testing framework for Ruby. It tolerates all code, whether it exhibits behavioral challenges or not. It never uses the words "test" or "failure", which would imply a value judgment, or "assertions," which would imply an absolute truth. Instead, it treads softly around code and espouses preferences.
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.