Noisy is a free app (OS X 10.5 or later) that generates pink noise or white noise, masking background chatter and other distractions. Noisy is based on the old Mac app Noise, which never became a Universal Binary.
One can get the benefit of noise by running SimplyNoise in a browser or by downloading a SimplyNoise MP3. I have an hour of pink noise on my iPod, which has been a concentration-saver in coffeeshops. But I think it’s especially nice to get some noise by running a tiny app. To the anonymous developer who turned Noise into Noisy: thanks.
[Without pink noise, I’d get nothing done in my office.]