Closed Source vs. Open Source
It's the age old question of whether to go the proprietary route, or to go the open road of open source. Let's get a few key difference out of the way first. Platforms such as Kentico and Ektron are considered closed source because their platforms are like walled gardens: They have x amount of developers and architects on their payroll that work to build websites for clients and they don't let outside developers use their code or integrate their plug-ins with other CMS's.
Platforms such as Drupal, DNN, and WordPress are considered open source because there's a vast community of developers that support each (Drupal alone has over 30,000 developers in its community.) Open source also relates to open source code, which means that these platforms make their code and extensions available to anyone who wants to use them. So if you're a Drupal developer, you can integrate any number of Drupal's plug-ins (such as their e-commerce platform) free of charge, or, you can easily integrate paid third-party platforms (such as Salesforce CRM) into your overall digital ecosystem.