Leap - With Leap you find things based on your natural memory of that file.
Managify - Create & organize all your documents in a single platform.
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Sismics Docs - Lightweight full-featured document management system 📁
Elyse - The free version allows up to 30 tags.
Yojimbo - Yojimbo makes keeping all the small (or even large) bits of information that pour in every day...