Quicksilver is a computer utility software program for Mac OS X, made by Blacktree Software and distributed freely. It is essentially a graphical shell for the OS X operating system aimed at increasing user efficiency. It allows users to use the keyboard to rapidly perform tasks such as launching applications, manipulating files and data, running scripts, or sending e-mail. It is similar to the Mac OS X applications LaunchBar and Butler, but uses a different interaction paradigm. Although it is a complex application, it is centered on a simple three-panel interface, called the "command window": the user performs complex tasks using simple, configurable key-combinations.