It could seem that Soundrop is an application like many more to create music on an iPhone. Nevertheless it isn't so, because you are going to compose the music based on a series of lines that you are going to draw on the screen.
How Soundrop works is very simple, because you will only have to touch the screen and drag your finger over it to draw a line. Then place as many droppers as you want and let the drops bounce off them, thus creating new sounds and melodies with the noise generated, with the possibility to add or eliminate lines at all time, as well as to edit features which influence how the drops bounce, like gravity and air resistance.
Download Soundrop on your iPhone and have a good time creating melodies.