Ramsophone - A generative art/music machine. (Be sure to refresh!)
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Generative Art in Go - Learn the basics of algorithmic art with the Go language
WaveShop - Open source audio editor
Big Art - Discover street art
TwistedWave - TwistedWave is one of the unique audio editors that allow you to edit your music file online without any installation.