TagSpaces - TagSpaces is an open source platform for personal data management. With TagSpaces you can manage and organize the files on your laptop, tablet or smart phone.
Tagger - Tagger is a small application for OS X that can be used for quickly adding arbitrary textual tags...
allTags - allTags is a free, tag based file management application.
Leap - With Leap you find things based on your natural memory of that file.
Elyse - The free version allows up to 30 tags.
NiftyBox - Nifty Box is a tagging application for the mac.