Leap - With Leap you find things based on your natural memory of that file.
Eagle App - Unify your creative inspiration in one place. Store anything – inspiring images, design mockups, illustrations, screenshots and more.
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Pixave - The ultimate image organizer for the Mac.
Elyse - The free version allows up to 30 tags.
Ego - Ego gives you one central—and lovely—location to check web statistics that matter to you.