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.
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.
Slingscold - Slingscold is a lightweight application launcher similar to Launchpad in Mac OS X.
DockbarX - DockbarX is a standalone dock that groups and launches applications.
kupfer - Kupfer is a command tool heavily inspired by https://alternativeto.