DFS

Finally, we have Drupal 5 released officialy. It was already available sometime earlier as release candidates one and two for testing stability, correctness and performance. Today, January 15th, 2007 which also happens to be the 6th birthday for this amazing open-source CMS sees this version being released.
A truly awesome CMS that provides a solid base from which you can make customized modifications for your site while also retaining the advantages of using a CMS. http://drupal.org/ provides more than I can ever write here.

Personally as for me, this is the most powerful open-source CMS mainly thanks to the clean api system. Requires knowledge of php/mysql though if you want to make those changes quick and fast by yourself. Almost all nodes and modules(including fields inside those) can be accessed directly and used which makes it that much easier to customize and build content however you want it to appear on the website. Loads of people out there who contribute with modules that they create, you will most definitely find ones that suit you and it is relatively easy to find someone among the huge talent-pool at drupal to build you one that does not exist.
BTW, hereafter all major versions will follow 6.x, 7.x, 8.x, etc. sort of numbering. Prior to this, they followed 4.1.x, 4.2.x, etc..