I'm wondering if anyone knows of a Content Management System of some sort that can assign multiple categories/variables/attributes to content items, and then allow the user to drill down ala NewEgg's navigation, narrowing his "search results" as he goes. The attribute list the user is presented with would have to be automatically generated, and when adding new content, the available categories would be presented to the author, with the option of adding a new attribute as needed (as opposed to the author typing whatever keywords might come to mind, resulting in duplicate attributes due to negligible differences, such as "Review" vs. "Reviews").