Coffitivity works online and includes three background ambience of a cafe, lounge, and university undertones. Iphone and Android app available, as well as a Google Chrome extension. Works via their site as well.
Similar to ZenCast, you can mix and match sounds to what you enjoy. This includes 'white noise' and ambience of libraries, cafe, and even a purring cat. Find their Android app, Soundscraper.
Noisli includes sounds for nature and white noise. They have settings for relaxation as well as productivity. Noisli includes Android, iPhone, and Google Chrome extension downloads. Works via their site as well.
ZenCast includes nature ambience sounds where you can mix and match sounds to what you like best. Currently, they are working on an android app. This works via their web site.
Rainy Mood provides ambience of rain with thunder, but also includes music depending on the day. This includes Android and iPhone apps to download.