Zeus is quite a useful tool when working with larger rails applications, or other larger ruby applications for that matter. Especially as it reduces the time to open a interactive environment for the project and makes the whole development process much more fluid. Combining it with Emacs power to send pieces of code directly from a buffer to be executed in a ruby process this is quite a nice way to explore and work. To quickly get access to a Zeus console simply drop the following in your Emacs configuration.
(add-to-list 'inf-ruby-implementations `("zeus console" . "zeus console"))
Maybe my suggestion to add this to inf-ruby will be added, but even if not it’s simple enough to get a console with this via C-u M-x inf-ruby.