Watir, pronounced water, is an open-source (BSD) family of Ruby libraries for automating web browsers. It supports your app no matter what technology it is developed in. They support Internet Explorer on Windows, Firefox and Chrome on Windows, Mac and Linux and Safari on Mac.
This is a meta-gem for having a convenient way to get all the necessary libraries with a single command:
gem install watir
Visit http://watir.com or refer to each gem's own README for better understanding of how to use these libraries.