Forum script that allows each thread to be categorised


I’m looking for a forum script that would allow users to associate a thread to one or more categories.

For example, in a forum about PCs, when creating a new thread, they could select a PC make / model from a drop down menu.

This would allow for a dynamic list of threads about a specific PC model across all forums.

sitepoint’s forum offers ‘tags’, which isn’t far off what I need.

Any ideas?