YARD
YARD is a Ruby Documentation tool. The Y stands for "Yay!"
...). Most importantly, it's really easy to do! There are already plugins that support frameworks like RSpec, DataMapper, Sinatra, and support for others are in the works. YARD is the only Ruby documentation tool that supports storing metadata alongside your documentation. This metadata can be used to create consistent documentation in any format you wish. YARD also comes with a powerful templating system to quickly modify existing templates.