Brownie

Brownian noise sounds more mellow and pleasant than pure white noise and is really good at masking sounds that have a bass component, like dogs barking, people talking, machinery or traffic, for example. Running through any halfway decent sound system, this should help you get uninterrupted sleep (I also tend to dream more and better with this running) or fully focus on any tasks that need concentration.

As a bonus, this app also produces static on the screen (while that is turned on - it does go easy on the battery while the screen is turned off).