Smule has an app called AutoRap
Here's a couple of my tunes. Having fun with it.
Make It http://khush.smule.com/autorap_52ef9d792f7a6&v2
Laying in the Sun http://khush.smule.com/autorap_52ee7e73e593b&v2
v http://khush.smule.com/autorap_52ee7e4c4b32d&v2
Feed Your Head Yo! http://khush.smule.com/autorap_52ee7dbbc1396&v2
Building http://khush.smule.com/autorap_52ee7d3b3bf77&v2