Slingscold - Slingscold is a lightweight application launcher similar to Launchpad in Mac OS X.
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.
Listary - Listary is a revolutionary search utility for Windows
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.
dmenu - dmenu is a dynamic menu for X, originally designed for dwm.