Drupal

Drupal is a free, open source CMS (content management system).

Drupal has numerous advantages. Among other things, setting up a site is very quick, it is modular and its API (application programming interface) is very robust.

In terms of how it functions, Drupal is programmed entirely in PHP. It is built around modules that all fit around a very light core. In a way, each module is a kind of function library which enriches the application and increases its potential.

One of Drupal’s strengths is the modules’ ability to interact with each other. The flipside of this flexibility is complexity. Drupal often proposes one or more solutions to solve the same problem.  Furthermore, the hardest thing is sometimes finding "the" module that best meets your needs. 

Another point setting Drupal apart from other CMS is that the site and its administration interface are closely linked: administrators produce their content in the same (or similar) graphical environment to visitors. This functionality can be unnerving at first, but is particularly productive and intuitive after the initial period of adjustment.