Drupal is a very powerful Content Management System (CMS) that has a well-designed taxonomy module. Taxonomy is the system of categorization and classification of things. In Drupal's taxonomy, you can define multiple vocabularies and the terms in those vocabularies can have multiple sub-terms. This site is set up that way with the high-level terms being general concepts such as "Programming" and "Technology." The one thing I wanted that it did not do out of the box was to show sub-categories as an additional navigation menu when you clicked on a parent category. It's not to hard to implement if you know how. Read on for the code snippets.