The to-do list app was created at Rails Girls 2015 in Cracow to show my participants how to build Rails applications. There's also a fancy feature to close or open tasks.
To setup the project locally clone this repository and type bundle exec rake db:migrate. If you want to create an application from scratch you may do it on lite.nitrous.io without setting up your own environment.
If you are interested in the game Ruby Warrior it's worth to visit this blog (especially in case when you can't figure out a solution).