This is a very interesting attempt creating a set of virtual turntables in your browser. The deck has a pretty basic set of volume controls, a crossfader, and some built-in effects, controlled in a parametric box below each turntable.
The website is seamlessly integrated with Soundcloud, so you can drag and drop any file that you find or upload yourself. You can even do some basic vynil scratching with the mouse or trackpad.
The webites creators say that they are in the very early stages of beta testing and if they truly want to create cloud based DJ mixing (which they say they want to do) there would have to be quite a few improvements (such as beat-matching, support for external control surfaces and support for multitouch)
Still, it is a very fun, educational tool and the only one of its kind on the web.