Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
Scherlokk - Mac OS X application. Simple and user friendly, Scherlokk will find your media and missed files - quickly.
Listary - Listary is a revolutionary search utility for Windows
Tembo - Tembo: Easy and Effective Searching
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.
Synapse - Synapse is a semantic launcher written in Vala that you can use to start applications as well as find and access relevant documents and files by making use of the Zeitgeist engine.