Leap - With Leap you find things based on your natural memory of that file.
Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Listary - Listary is a revolutionary search utility for Windows
Elyse - The free version allows up to 30 tags.
Alfred - Alfred is an award-winning app for macOS which boosts your efficiency with hotkeys, keywords, text expansion and more. Search your Mac and the web, and be more productive with custom actions to control your Mac.