Drupal is a free open source framework and a content management system (CMS) which allows users to easily create, edit and organise all sorts of content. It is one of the most flexible and powerful CMS systems on the market and its usability has significantly improved with each new release.
Drupal offers all the standard features of a modern CMS and has active members who continuously develop and improve the Drupal core.
Out of the box it offers a built-in advanced taxonomy system that makes it possible to index and classify content according to predefined categories. This makes it possible to quickly link to different types of content on the length and breadth of classifications, and display related content in an easy way.
The Australian Government has introduced a government wide CMS system based on Drupal and this will certainly increase the adoption of Drupal nationally.
The most powerful and flexible CMS out of the big three. It has received criticism for being difficult to use.
Drupal needs to be carefully managed and capacity planned to ensure it scales for your environment