Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
DockbarX - DockbarX is a standalone dock that groups and launches applications.
Slingshot launcher - Lightweight, stylish Launcher for Elementary OS
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.
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.