What programs have the most advanced file tagging functionalities? To clarify: I am not talking about multimedia tagging, where the metadata fields are fixed. I am talking about free-form tagging of any files, with tag fields arbitrarily defined by the user, for managing large collections of heteronegeous files.
Functionalities such as logical operations with tags (set theory and such), wildcards in the tag queries (e.g. include all tags that match abc*), virtual folders based on tags, etc. would especially be very much appreciated.
Any ideas related to tagging programs, even if not currently implemented in a program, would be welcome in this thread.