Drupal is an open source content management system (CMS) that can also be used for knowledge management as well as business collaboration. It is a free software package that can be deployed on web servers to attain the mentioned functionality. For further information check out the Wiki. Drupal has been at the forefront of open srouce enterprise class content management. Take a look at a list of Awards won by Drupal. Here are some high profile organizations that utilize Drupal.
Top C Web Solutions focuses on the integration of the Drupal based websites/online applications with business intelligence and web analytics. This incorporation of measurement with content management allows for rapid deployment and return on investment calculations.
Acquia partnership for enterprise level implementation expertise.