Need some background, natural sound for your coding – browsing – reading sessions? Or a simple, relaxing, white noise generator? There are plenty of sites that offer this service, here some of them:
Noisli: Set different elements power (water, wind, fire and others) and compose your melody. Available for mobile devices also.
Coffitivity: able to focus only when on a public cafe? Reproduce the same background noise and make things happen! For mobile too.