A relatively new feature availaible in Ruby on Rails is a Folksonomy GEM that makes adding tagging to your web apps relatively trivial. I do quite a lot of posts about tagging and Folksonomy; I suppose being such an avid user of the del.icio.us tagging site in both my personal Internet usage and relative to this site makes me particularly interested in it. Rails is also something I and a lot of other people are interested in and this is a handy little intersection of the two technologies.
More information on the acts_as_taggable plugin can be found at the Rails Wiki.
