Rails-katas is a project mainly written in Ruby, it's free.
Practicing rails one day at a time
The Ruby Katas is my journey to enlightenment in order to master Ruby on Rails. The goal is to learn the Ruby on Rails framework, tools, techniques, patterns and anti-patterns. We also practice some culture. Testing is essential in the quest to learn and do great things in the language.
The katas are independent projects that I perform one or more times. Each kata builds up some knowledge of Rails and builds upon itself.
Some katas are original exercises, other are taken from books.