Ruby on Rails is an open-source project hosted at www.rubyonrails.com. This site not only hosts a great deal of code, but also much documentation, demos (including movies) and mailing lists for Rails enthusiasts.
As of this writing, an excellent printed book about Rails has just been released by the Pragmatic Programmers. Information about both the book and its current status is available at www.pragmaticprogrammer.com.
O'Reilly's “OnLamp” site has published several articles about Ruby on Rails. One good introductory article is at www.onlamp.com/pub/a/onlamp/2005/01/20/rails.html?page=1.
The Ruby home page is at www.ruby-lang.org. This page has many links to other sites, including tutorials and documentation, for the Ruby language.