DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
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.