Drupal is an open-source content management system. It's developed and maintained by thousands of users and developers. It allows users to easily publish, manage and organize their content on a website without the need of special tools or a team of web developers.
Drupal combines the functionality of a community web portal, a personal website, a blog and countless other web applications. It has the ability to create forums, newsletters, peer-to-peer networking, picture galleries and much more.
In short, Drupal provides all the functionality to bring your vision of a website to life.
For more information about Drupal, see their website.