Sorry for any misunderstaning, I understood you were willing to pay. You can import images into ElectricQuilt, many makers now specifically make files of their lines available, so that half of the equation is pretty easy even using different lines available from different sources.
If there is an app that does what you want, I don't know it yet but if it is out there, it is likely that someone here knows about it.
ElectricQuilt seems pricey but it is very powerful, the equivalent of a CADD program. In addition to letting you play with your designs and fabrics, it can help calculate yardage, quickly scale a project up or down, print out templates for piecing or paper piecing, the benefits go on and on.