Drupal is a free (licensed under the General Public License (GNU), Version 2 or later), community-powered, open-source Content Management System (CMS), which allows creating websites of many types. It's a great tool for both, users with no technical background, as well as top-notch developers, to use it for building complex websites and web applications.
Some examples for popular companies and organizations that decided to leverage Drupal as their content management system are FedEx, Symantec, MTV, and Duke University. The list is long, and you can find out more at http://drupal.org/case-studies or http://www.drupalshowcase.com.
In this chapter, we will cover: