Rinari Is Not A Ruby IDE.
Well, ok it kind of is. Rinari is an Emacs minor mode that is aimed towards making Emacs into a top-notch Ruby and Rails development environment.
IMPORTANT NOTE: This package is unmaintained these days, and users should consider an alternative, e.g. the projectile-rails package.
For a screencast of Rinari see http://vimeo.com/2854412
For the latest version see http://github.com/eschulte/rinari/tree/master
For somewhat outdated installation instructions and documentation see http://rinari.rubyforge.org
For discussion of Ruby on Rails related Emacs development see http://groups.google.com/group/emacs-on-rails