Drupal es ...
1 A platform for quick website assembly
It allows you to build websites in a matter of weeks, with minimal custom programming. There is no need to start from scratch every time you build a new site.
2 Huge in scalability
Some of the largest, most visible, and most highly trafficked sites in the world are powered by Drupal, including examiner.com, whitehouse.gov, and 71 of the top 100 universities.
3 Freely extendable
Thousands of modules at http://www.drupal.org/ allow you to build amazing sites with little to no programming; its well-documented API lets you tailor it to your needs through custom code.
4 Built for social publishing
Drupal is a multi-user CMS by default, which allows highly precise access controls between users. Drupal can even share logins and content with Facebook, Twitter and others.
5 Open to showcase your brand
Drupal's presentation layer ("theme") gives designers the freedom to create highly usable and interactive experiences that engage users and increase traffic.
6 Flexible in deployment
Drupal offers several ways to deploy multiple sites with unified codebases and databases. Many companies manage multiple Drupal sites, while some manage hundreds on other platforms.
7 Loved by a thriving development community
Nearly a thousand people contributed to the Drupal 8 release, with many thousands more working on add-on modules, security monitoring, documentation, and much more.
8 No software acquisition or licensing costs
As open source software, the Drupal package has no licensing rights. Your money goes towards the things that make your site unique.
9 Fanatic of following standards
Drupal integrates very well with other systems taking advantage of existing standards. It connects to web services, delivers content to mobile devices, and supports various authentication and authorization schemes.
10 Ideal for sites that require high security
A dedicated security team, along with the vast community of Drupal developers and administrators, finds and patches issues often before they are exploited in the wild.
Learn more at: http://www.drupal.org/