Even though there's thousands of Drupal modules freely available, sometimes you need something special and specific to your business.
Drupal isn't just a Website Content Management System (WCMS), it's an application platform. It can be used to build software applications that are hardly websites in the normal sense of the word.
Features that are required by almost all software like user authentication, role based authorization and database backed content editing are provided out of the box by Drupal, so it's possible to build custom applications much faster using Drupal than with purely custom development.
