Government entities use open source solutions because:
Cost: Open source entirely free and doesn't have licensing fees
Security: Supporting communities identify and address vulnerabilities fast
Stability: Features aren't tied to a vendor's product roadmap or agenda
Drupal is an open source content management system that powers websites for government organizations like the NIH, City of Boston and City of Los Angeles. Check out Boston's story, why they chose to build Boston.Gov on Drupal and how Acquia helped them.