OnlineSequencer.net - OnlineSequencer.net is an online music sequencer that allows users to create beats and music tracks.
WaveShop - Open source audio editor
AudioSauna - AudioSauna is a full-featured audio workstation for making music online.
TwistedWave - TwistedWave is one of the unique audio editors that allow you to edit your music file online without any installation.
Jummbox - A modified Beepbox that have more stuff then Beepbox. It can be used just like Beepbox. The features of Jummbox is the same of Beepbox's features, but Jummbox have more stuff to offer.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.