If you want using this gem, you need add
gem 'api_flashcards' , git: 'git://github.com/Sivard/api_flashcards.git'
Mount engine to app
mount ApiFlashcards::Engine, at: "/api_flashcards"
to config/routes.rb
if you want test this engine, rename card.test.rb and user.test.rb to card.rb and user.rb
This project rocks and uses MIT-LICENSE.