Durpal is the most advance CMS in the market today. It's definitely meant for developers rather than non-technical users. It has one of the most complex and comprehensive software framework that allows developer to build just about any form and shapes of website. Drupal is famous for the steep learning curve for developers. However, once the developers master the development framework, Durpal offers a very large scope of possibilities for customisation!
It's also a great choice for creating integrated digital frameworks. You can extend it with any one, or many, of thousands of add-ons. Modules expand Drupal's functionality. Themes let you customize your content's presentation. Distributions are packaged Drupal bundles you can use as starter-kits. Mix and match these components to enhance Drupal's core abilities. Or, integrate Drupal with external services and other applications in your infrastructure. No other content management software is this powerful and scalable.
The Drupal project is open source software. Anyone can download, use, work on, and share it with others. It's built on principles like collaboration, globalism, and innovation. It's distributed under the terms of the GNU General Public License (GPL). There are no licensing fees, ever. Drupal will always be free.
License: GNU/GPL license.