As referred to in the discussion of this site's data model, Drupal includes a flexible user model complete with fine grained control of who can or can't create, edit or see any particular type of data that has been created on your site.
Because all components of the software required to run a Drupal site are open source, you are free to set up a Drupal site wherever makes sense to you without necessarily incurring licensing fees (although you might decide to install it using a proprietary OS, thereby incurring some costs). This flexibility to use the software where you need it also implies that you can decide where and how you want to store and manage the data you produce using the site. You can run this on you own hardware or pay a web hosting provider for a virtual server and run this software there.
None of this is to say that you can run a web site for free. Web site management takes time, effort and resources. But the flexibility to create the site and the data where you want does allow you to think about how you would like to manage the information created and who should be in the conversation to make those decisions.
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