Yes, I’m using the term “app” instead of ye olde “application” now, just to sound cool.
Chrome recently introduced a feature, which allows you to see which tab makes noise. This is useful if you have a lot of tabs open, and a Flash ad runs berzerk, so it will ruin your music or just annoy you to hell.
Did you know, that Windows has the same feature, just on application-level?
Since Vista, you can click on the speaker button in the “System Tray” (This term is wrong, it’s actually the Notification Area, but people seem to know it by this name), then choose “Mixer” (in my german Windows).
Then you can see, that currently Skype uses sound, for calling the famous Echo service.