Started for blogging, wordpress has grown into a wonderful content management system that is search engine friendly and in the main, free.
As an open source cms, it has led to some of the worlds top designers and developers to contribute to its functionality. Developers have created WordPress plugins that have added everything from ecommerce capabilities to stringent security. Designers have created themes that cater to photographers right through to designs for law firms.
But what about the competition?
Another open source application, Joomla offers a middle ground between Drupal and WordPress and the ability to structure more complex and flexible sites than wordpress. A strong user community help this great cms. Supports ecommerce and social networking sites.
Known for its strong taxonomy and ability to create complex content, Drupal is another open source cms. Requiring the most technical expertsie of the three, it is also capable of creating the most advanced sites. A great developer lead community, Drupal is well suited for complex data sites like multiple user community sites.