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.

Features:

• Real-time audio synthesis
• Expressive musical pattern system
• Efficient object-oriented programming language implementing features of modern functional languages
• Expressive multichannel support (massive numbers of input/output streams)
• Supports diverse stylistic and technical requirements
• Interacts with other systems using MIDI or Open Sound Control (OSC)
• Essential part of numerous art and science projects

Here is a short demo video:
http://www.youtube.com/watch?v=4tiEfHaRszU

New in 3.5rc1:

• New help system, browser (HelpBrowser) - jle/jli
• Command and feature changes
• Various bug fixes
• Complete revision changes here