Relaxia — Health & Fitness — Free ($3.99 unlock)
The App Store is full of things that play white noise or some ocean sounds to punch your ticket for the Sleepy Train to Snoozeville, but I haven’t seen one as good-looking and versatile as Relaxia. It has six noise “themes” with about eight sounds in each; you can play multiple files at once and adjust their volumes to make your own custom mix of sleep fuel, and you can set a timer so it’s not still playing in the morning.
Because it would really be awful if you woke up, thought it was raining, and then it wasn’t.