Tabbles - Tabbles use tags to organize and find files along with your colleagues.
Leap - With Leap you find things based on your natural memory of that file.
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.
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Elyse - The free version allows up to 30 tags.
TaggTool - The Personal File Tagging Utility.