looking for an app that does categories/lists...

hi... i need a quick/simple app/script the will allow me to create a master directory/list, and then create subcategories of the master categories, as well as the child categories... i'd also like to be able to move nodes/branches of the tree around as needed. i'm basically looking at setting up an app that's going to have an admin create the required categories/classifications, and then i'm going to allow users to be able to specify what categories/sub-categories they belong to. does anyone have any pointer to an app/script that could do the directory/categories portion of what i just described... i've looked through google/freshmeat/sourceforge/etc.. as well as some of the scripting sites without much luck... thanks bruce bedouglas@earthlink.net