DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
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.
TaskSurfer - TaskSurfer gives you all of the tools you need to manage things the way you want.
allTags - allTags is a free, tag based file management application.
HoudahSpot - Advanced File Search Utility for Mac OS X
Tabbles - Tabbles use tags to organize and find files along with your colleagues.