Update on March 18th: new extensions for Joomla has been added.
3 days ago, while in conversation with a large group of prominent WordPress users, I asked “What is the most powerful CMS plugin for WP on the market right now?”. Within hours, I got a lot of backlash from the community reassuring me that WordPress is already a CMS. To me, WordPress is very advanced & powerful blogging platform, but not quite a full fledged CMS, yet. However, WordPress codebase is built so that you can code any CMS features you want. It explains perfectly why WordPress has 29,873 plugins (at the time of writing), comparing to 7730 extensions of Joomla, and 14,764 modules of Drupal.