Rainy Mood is described as 'Mobile rain experience to help you sleep, study, and relax. The new Rainy Mood app has four fully-customizable rain scenes -- Classic, Ocean, Countryside, and Café. With stunning HD/48kHz 3D audio and algorithmic randomizer, your brain will naturally relax' and is an app in the sport & health category. There are more than 50 alternatives to Rainy Mood for a variety of platforms, including iPhone, Android, iPad, Web-based and Mac apps. The best Rainy Mood alternative is Blanket, which is both free and Open Source. Other great apps like Rainy Mood are Noice, myNoise, SoundAura and Brain.fm.
It's calming and very enjoyable.