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.
Tembo - Tembo: Easy and Effective Searching
xlunch - xlunch is a graphical app launcher.
Listary - Listary is a revolutionary search utility for Windows