Drupal core includes core modules which can be enabled by the administrator to extend the functionality of the core website.
Contributed Drupal modules offer a variety of features including image galleries, custom content types and content listings, WYSIWYG editors, private messaging, third-party integration tools, and more. The Drupal website lists over 5800 free modules (as of July 20, 2010), written and contributed to by the Drupal community.
A popular Module is CiviCRM, a powerful, web-based contact relationship management (CRM) system. It allows an organisation to record and manage information about the various people and other organizations it deals with