A collection of Ruby katas that I have worked on to gain proficiency in Ruby and to practice problem solving techniques.
"A kata is an exercise in karate where you repeat a form many, many times, making little improvements in each. The intent behind code kata is similar. Each is a short exercise (perhaps 30 minutes to an hour long). Some involve programming, and can be coded in many different ways. Some are open ended, and involve thinking about the issues behind programming. These are unlikely to have a single correct answer.
The goal is the practice, not the solution." - Dave Thomas