The taxonomy module is providing custom categorization of arbitrary content types.
|Taxonomies 1.4||5511||29 Feb 2012|
|Taxonomies 0.9||2985||5 May 2011|
|Taxonomies 0.8.1||809||19 Jan 2011|
|Taxonomies 0.8.0||115||14 Jan 2011|
This module would work nicely, if they would fix some urgent bugs. For example, you currently cannot use this module if you have plenty of users, as it has a bug that generates an additional query per user you have (it took ~15sec here to process a 'click' because we have 60k users) The developer does not seem to be very active lately, and this is sad, as I'd consider this module a missing core functionality :/