SuperCollider is an environment and programming language for real time audio synthesis and algorithmic composition. It provides an interpreted object-oriented language which functions as a network client to a state of the art, realtime sound synthesis server.
SuperCollider was written by James McCartney over a period of many years, and is now an open source (GPL) project maintained and developed by various people. It is used by musicians, scientists, and artists working with sound. For some background, see SuperCollider described by Wikipedia.