Djay, by Algoriddim, puts a pair of turntables and a mixer onto the touchscreen of the iPad. I have been playing with it for a day and it’s pretty awesome.
The iPad seems to be an obvious place for the app, which also exists on the Mac. Multitouch makes adjusting sliders, choosing music and — of course — scratching seem like you’re using a real (if very small) DJ setup, and an iPad full of MP3s is a lot more portable than a box of records, or even CDs.
I’m no DJ — when I used to have a bar I banned myself