Prior to my iPhone, I carried a variety of digital cameras. While quick and easy to shoot, I missed a few features that almost seemed easier using my older film cameras. Movement in an image was one of those features. The ‘better’ digital cameras did movement but the entry level units froze everything in time.
For the iPhone, there is Slow Shutter. Do you want to show movement going by like water over a waterfall or car taillights on the street below, it gets that handled.
Slow Shutter handles the other side of movement too… like a picture out the window of a plane or car where the foreground frame is still and the background moves by. The app provides a manual mode for you to completely control the shutter open time as well an automated option where you choose a length of time and how you want the movement handled and Slow Shutter does the rest. There is a single image result but the app holds many images that you can move through to adjust the final… like in the case of cars going by you can adjust at what point in the capture had the right amount of light trails.