dmenu - dmenu is a dynamic menu for X, originally designed for dwm.
Slingscold - Slingscold is a lightweight application launcher similar to Launchpad in Mac OS X.
Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
Mutate - Mutate is a simple launcher inspired by ...
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.
Scherlokk - Mac OS X application. Simple and user friendly, Scherlokk will find your media and missed files - quickly.