The quote says it all:
... an open-source (i.e. free) content management system that’s flexible and feature-packed. Over the last couple of years or so, it’s taken off as the go-to platform to run websites that require a lot of community and content management features. From personal blogs and brochure sites, to fully-featured social networking sites, portals, news sites, and e-commerce websites, Drupal has proven itself as the most robust platform currently available in the content management system market.
It then goes to showcase a list of 31 Remarkable Drupal Powered Websites, with screenshots.
Some of those are well known, others are new to me.