This site is running on Drupal, a powerful and flexible open source content management system which runs on PHP and MySQL. Drupal has a slightly steeper learning curve for development and doesn't have as much eye-candy in the back end as does Joomla!, but it more than makes up for that with its robust system of tagging (which is referred to as "taxonomy"). Where Joomla! requires categorization of content with one section and one category within that section, Drupal allows multi-tagging, hierarchical tags, and even free tagging where you can type tags on the fly. See my portfolio on this site for an example of multi-tagging: items are tagged with client name, client type, and project type, so each page can show up in multiple locations on the site, depending what the user is searching for.
