Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
Everything by Voidtools - Everything. Locate files and folders by name instantly. Everything. Small installation file. Clean and simple user interface.
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.
DocFetcher - DocFetcher is a portable German/English open source desktop search application.
DockbarX - DockbarX is a standalone dock that groups and launches applications.
X1 Search - X1's Lightning-Fast Search Software. Premium Alternative to Windows Desktop and Outlook Search.