Drupal is a popular free and open source content management system and written in php.
Drupal is the platform for web content management among global enterprises, governments, higher education institutions, and NGOs. Flexible and highly scalable, Drupal publishes a single web site or shares content in multiple languages across many devices. Technology and business leaders transform content management into powerful digital solutions with Drupal … backed by one of the world’s most innovative open source communities.
It is also describes itself as a Web application framework.
Drupal runs on any computing platform that supports both a Web server capable of running PHP and a database to store content and configuration.
Drupal comes in the top 3 most used content management system.