After a few years I still use Listary as my main search/launcher. It's very quick, has a very nice look and great system of filters and projects. There are problem with new version to be released, but I'm talking about version number 5.
Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
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.
Gnome Do - Simple, sleek, swift, smart. Do. GNOME Do allows you to quickly search for many items present on your desktop or the web, and perform useful actions on those items. GNOME Do is inspired by Quicksilver & GNOME Launch Box.
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.
Everything by Voidtools - Everything. Locate files and folders by name instantly. Everything. Small installation file. Clean and simple user interface.
Ulauncher - Fast application launcher for Linux. Custom shortcuts for web URLs and scripts.