Punakea is a Mac App designed to help you cope with the day-to-day struggle of managing your files. Complementing Spotlight, it allows you to tag your files and bookmarks, freeing you of the strict hierarchy of the Finder's folder structure. It's like Finder Tags, but with a tag cloud!
The official web page is hosted here.
More information can be found in the wiki.
Punakea has been originally developed by Daniel Bär and Johannes Hoffart from 2006 to 2013. At the end of 2013, Punakea has been made available as an open source project under the MIT license.