Tagit is described as 'File tagging and rating utility for OS X'. There are four alternatives to Tagit for Mac and Windows. The best alternative is RecentX. It's not free, so if you're looking for a free alternative, you could try Taglists or Tagger.
RecentX is an innovative launcher that gives you instant access to your files, folders, programs, websites & clipboard history. It automatically remembers your favorite & recent items so that you can launch them even faster.
TagLists is a small application for OS X that allows you to quickly see which files you've tagged with particular tags. It uses the OpenMeta tagging system, which means that it finds files that have been tagged with any of the applications that support OpenMeta.
Tagger is a small application for OS X that can be used for quickly adding arbitrary textual tags to files. It uses the OpenMeta system for saving tags, so the tags you add with it will be readable (and editable) by all the other applications that support OpenMeta.