Capistrano is a remote server automation tool, written in Ruby.
It can be used to deploy your Drupal website to any number of machines (environments).

I gave a similar presentation on DrupalCamp Leuven 2013 about Capistrano v2, but since Capistrano v3 is completely rewritten from the ground up it became even easier to start using it for web applications which are not Ruby based as this dependency is left out in v3.