DJs are a funny bunch, mostly preferring to use clunky old vinyl to work their magic, but technology rarely takes no for an answer and Traktor Scratch is no exception, offering traditional DJs who can't be separated from their Technics decks access to massive digital music libraries.
Put simply, Traktor Scratch is a simplified version of Traktor DJ Studio, which enables you to mix music without any special hardware. What the Scratch system adds is a very high-end sound card that enables multiple audio inputs, via which you can connect either vinyl or CD decks.
What's the point of that, you might ask? Well, you aren't just connecting playback devices to your computer, because Scratch comes with timecoded vinyl and CDs. The purpose of these is to allow you to control your digital music, and manipulate it as if it were a record. This is actually much simpler than it sounds, and you can combine CD players and vinyl as you see fit. Up to four decks can be used too, which is really quite incredible.
That means you can scratch, move the needle and generally use your MP3s like a giant vinyl collection. If you have CD-Js, you can even program all of the buttons on the unit to perform different software functions using MIDI over USB.
You get the software, Audio 8 USB soundcard and the timecoded vinyl and CDs in the box, which is available now for about £400 -- you'll have to provide your own turntables though. –Ian morris