Splice Beat Maker - Make and share beats in your browser
Traktor Pro - Flagship DJ software with four decks and a stunning range of creative features for maximum freedom in DJing.
Ramsophone - A generative art/music machine. (Be sure to refresh!)
Mixxx - The most powerful free DJ software in the world.
Google Music Lab - Interactive experiments that use the Web Audio API
VirtualDJ - Virtual DJ Software - MP3 and Video mix software for DJs