dmenu - dmenu is a dynamic menu for X, originally designed for dwm.
Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
Gnome-Pie - Gnome-Pie is a circular application launcher for Linux.
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.
Slingscold - Slingscold is a lightweight application launcher similar to Launchpad in Mac OS X.
Circle Dock - The idea behind Circle Dock is that the dock should appear where your mouse is instead of you...