Drupal is one of the most preferred open source solutions because of its high degree of flexibility and extensive community (more than 630,000 users!). The platform easily serves small blogs and big enterprises and features a robust base of plug-ins and add-ons to tackle any project.

While it is not the simplest of the CMS products highlighted here it is arguably one of the most robust. Drupal is often regarded as a Content Management Framework where, depending on which modules you install on top of the core, you can have anything from a simple blog to an extremely complex, large scale, website.