An oldie but a goodie. Ryan Bates' (of Railscasts.com fame) excellent remake of David Heinemeier Hansson's original 15 minute Ruby on Rails blogging app demo.
Ryan Bates' re-make of the Rails blog app demohttp://yehudakatz.com/2009/08/26/how-to-build-sinatra-on-rails-3/
How to build Sinatra on Rails 3