Drupal is a flexible open source content management system (CMS) that can be used to build large websites with many features and customizations. It has over 9,000 modules, 1,000 free themes, and strong community support to customize any site. Drupal also offers search engine optimization, multilingual support, security updates, and dynamic content displays through modules. With 15+ years of ongoing development and use by millions of sites including whitehouse.gov, Drupal ensures a future-proof and reliable CMS.