1. It's a free of cost and an open source software: In Drupal large number of themes, modules, plug-ins and core software functionalities are available free of cost which reduce web development cost.
3. It is fully enterprise -class software: In terms of features like: reliability, scalability, security, manageability and availability of resources it's a better software. Its CRON service is one of the best features that I like most. CRON is an automated service which runs after an interval every time and checks for the updates and various issues to make your website secure and bug free.
4. It also supports extensive API: In Drupal an extensive API support like: facebook, twitter, youtube, linked-in, Google apps, Google Webmaster, Google Analytics, etc. We can create own modules by using well-documented API too.
5. It's also SEO Friendly: As we know search engine optimization is playing an important role for the promotion of websites and online marketing strategies for any website or company. Drupal enables us to develop SEO friendly websites. It provides enormous facility to display website content as per search engine like.
6. Helpful in developing Responsive or mobile friendly website: Drupal also provides enormous flexibility to develop mobile friendly websites. Drupal has great themes of today's most popular responsive website designing frameworks such as Bootstrap, Foundation, and Skeleton. So, if you are a UI developer then you can customize it at its fullest and if you are not then you have ready to work themes in Drupal for you.
7. Best modules which make Drupal a super heroic skill CMS: Few modules of Drupal are the pillar of success for it. I want to name out here for you, and they are Ctools(Chaos Tools), Views, Token, Path Auto, Meta SEO, Panel, Rules, CKEditor, Views Accordion, Views Slideshow, IMCE, Views Carousel etc are just few names those making Drupal a leader to developer rich-featured websites without writing a single line of code for most of the websites.