One of the most (in)famous marketing ploys of the not-so-recent past was the .NET pet store, where Microsoft showcased the new .NET framework in an ASP.NET web application with similar functionality as the erstwhile Java PetStore, using vastly less code. It also performed and scaled much better on all benchmarks conducted by Microsoft.
Sure enough, there's a pet store done in Ruby on Rails as part of the ThoughtWorks Commons project, used mainly for scalability "shootouts". Check it out and poke around to learn how things
are can be done. There are actually two pet stores with PetStore2 more of an AJAX/Web 2.0 site. As complete sample rails apps for free download seem to be hard to come by here's one option that can be used for learning as well as for speed tests. Hope it helps.