Leap - With Leap you find things based on your natural memory of that file.
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
TaskSurfer - TaskSurfer gives you all of the tools you need to manage things the way you want.
Elyse - The free version allows up to 30 tags.
IDocument - Feel powerless of your documents chaos in your Mac?
Benubird PDF - A leading PDF developer since 2007, with PDF productivity tools like Debenu PDF Tools, Debenu Quick PDF Library, PDF Aerialist and Aerialist Pharma PDF.