Since the appearance of Drupal 5, Drupal distributions have been a steadily growing option in the world of Drupal development. A distribution is a prepackaged copy of Drupal core along with a premixed recipe of additional modules, themes, libraries, features and install profile scripts. When you install a copy of Drupal, you basically get a pre-built blogging application. When you install a Drupal distribution such as Open Atrium, you will have a full-fledged open-source project management application.