Since 2006, we have had very good experience with one of the largest open source content management systems in the world: Drupal. From a basic CMS this software package has turned into a very powerful framework for various web applications around the globe.
Our own products, such as edubreak®CAMPUS, are also developed on the basis of Drupal. The online environment developed for the DOSB in 2012 to collect licensing statistics for all members of the DOSB was also implemented using Drupal. Finally, since 2013, the DOSB's large education network for the exchange of all those responsible for education in German sports has also been implemented by our team on the basis of Drupal.
The big advantage is that the basic package of Drupal alone provides an excellent starting point for most of the current challenges. These include person-centeredness, social sharing and rich, portable content. Full control over the source code ensures both certainty about the actual functionality and operations within the modules (and the entire environment), and the ability to flexibly customize them for your own needs. Finally, most and most important modules are also actively maintained, developed and provided with security-related updates by the Drupal community.
For us it is very important not only to profit from the open source community, but also to contribute something ourselves. In the past, we founded our own (sandbox) projects and made them available for free use with open source code (e.g. as3drupal), as well as submitting suggestions for improvements to existing projects.