A content management system, or CMS, is a web application designed to make it easy for non-technical users to create, edit and manage content on a website. Not only do content management systems help website users with content editing, they also take care of a lot of "behind the scenes" work such as:
Automatically generating navigation elements
Making content searchable and indexable
Keeping track of users, their permissions and security settings
Drupal is a free and open source software package that allows you to easily organize, manage and publish your content, with an endless variety of customization. Drupal's key feature is its modularity that makes it easy to add a broad range of features and services. When you learn about a new trend in web development or a new cloud service, chances are big that "there is already a module for that". Of course, you can easily extend your Drupal site with a custom developed module as well.
The Content Management System of the iText website is Drupal.