Drupal core
Drupal core is the foundation of every Drupal application. It represents all out-of-the-box Drupal features and contains the framework every Drupal application is built on. It has the most rigorous contribution process while having the largest amount of contribution activity.
While Drupal itself, as an open source project, is free, it should be viewed more through the perspective of “free like a puppy.” Drupal code is freely available, and there is a vast community helping to maintain and support it. However, Drupal applications require ongoing maintenance. Major and minor upgrades need to be performed to update the code. The underlying servers and platform need to be maintained as core evolves its platform dependencies. The community helps promote efforts to more seamlessly and automatically perform code updates, but adopters are still largely responsible for running their own platforms or picking a commercial PaaS offering. This takes ongoing work and...