title: How to remove gem from Ruby on Rails application?
body: <p>I have installed a gem on my Rails application (devise). After I installed the gem, I realized that I don't need it.</p>
  
  <p>I want to remove the gem, its dependencies and the files it created on my application. In other words, I want to restore the system to what it used to be before the gem. How can I do this? (I'm using Ruby on Rails 3.)</p>