Ryan and I recently presented at the Drupal Business Day, the first time that the global event has been held in Singapore. The guys at Pixel Onion (Kiat & SJ) did a fantastic job putting the event together and thanks to them for extending an invitation for us to speak at the event.
It is a free, mobile friendly, open-source content management system and framework that is used to build many modern websites ranging from blogs to media, enterprise, political and government websites. It is used in at least 2.1% of all websites worldwide. Examples include the White House and The Economist. The platform also scales well to support millions of users.
For a list of websites built on Drupal, check out the Drupal showcase.
Check out this useful list of modules for community building.