Download Free [Question] App that allows me to overlay one music track with another

I have been looking for an app that will allow me to overlay one music track over another, so i can listen to both at once, one in the background, one in the fore. is there anything available that will let me do this?

Download link http://www.mannesoth.com/download/19/12964000/[Question] App that allows me to overlay one music track with another