CiviCRM is a CRM (client relationship management) module for Drupal. As a Drupal module it's huge (more code that Drupal core) and demanding (memory, processor), and it looks funny. Well, that's because it's not really a Drupal module, it just exposes itself to Drupal using some of Drupal's clever glue ("hooks"). In fact, CiviCRM has its own goals, development team, mysql database and philosophy that's quite different from Drupal. It even works with another CMS (Joomla/Mambo).