Check this vid out. omg its really cool. just buy a cheap tablet with at least 1.5gb ram ans 2-core (or faster processor as you'll see how his lags.

Here's the review of the app.

 

I actually swapped out my head unit for a nexus 7 tablet. It was a fairly easy install (needed a dremmel for some trimming around the dash kit) and the nexus7 is almost a perfect fit in the dash kit opening. I am running the audio through a Clarion EQS755 ( ) which separates the audio signal to the front and rear speakers, plus allows connection of a separate audio device through RCAs and 3.5 jack connections. I did notice that the tablet can die if left in the car over a cold weekend, so I trimmed away a piece of the dash kit so I turn the tablet on and off with out having to pull it out. It may not be for everyone, but I enjoy the setup ;-)