Kontrol One is a usb powered modular Dj MIDI controller wich functions as a deck. It actually can be used to control up to 4 virtual decks at once on Virtual DJ, Traktor and Decadance. Of course you can map it on any other DJ software. It doesn't have a soundcard or a mixer section. It's an amazing little beast!!
I bought it when I was looking for a small and lightweight controller for at least 2 decks that I can carry in my laptop bag but I missed!! It's actually a big and quite heavy controller, it is a well-built metal construction with lots of plastic buttons and rotary encoders. It's tall so it sits perfect next to my Technics turntables and the mixer.
It has a simple layout with a touch sensitive, high resolution jog wheel in the middle, a pitch fader on the to left, 4 hot cues, loop and sampler buttons with shift functions. Also it has 4 rotary encoders with LED rings and push to switch function for direct control over effects, filters, and samplers. On the top left corner there is the deck select knob which gives a nice steady feeling when changing control decks. I've also mapped the top right encoder to loop functions. It is mainly usb powered but it offers a 6V DC input if you want to use more than 1 of them on a hub in your laptop.
So, If you want a deck controller to sit next to your mixer it is the ideal choice. If you want 2 of them even better!! And if you need a mixer also there are the DJ-Tech Hybrid 101/202/303 Packages which bundle an analog mixer with integrated USB sound card and two or four separate control surfaces for each deck in a flight case!!