Wikipedia
LaunchBar is an application launcher for Mac OS X. It provides access to user's applications and files, by entering short abbreviations of the searched item's name. It uses an adaptive algorithm that 'learns' a user's preferred abbreviations for a particular application. For example, after training, Adobe Photoshop may be launched by simply typing 'pho' and Interface Builder can be opened by typing 'ib' even though that sequence of characters does not appear anywhere in the name of the application.
LaunchBar also provides capabilities beyond application launching, such as file management and piping the current selection to a command line utility, along with clipboard management and a built-in calculator.
LaunchBar is distributed as crippleware shareware - full usage of the application requires paying the registration fee, but up to 7 abbreviations may be used per session without paying anything.
According to user interface researcher Bruce Tognazzini, "LaunchBar should be able to outperform a visual interface for complex, repetitive switching sequences by an expert user"