If you've ever booted up your mac in a crowded place you know how annoyingly loud and embarrassing the boot sound can be. Apple gives you no way to adjust the volume of this sound. I usually try to cover the speakers with my hands to mute the sound. But there's a better way now. An app called Psst lets you set the volume of your computer during the boot so that you can turn down the volume when booting. It doesn't work on every model of the Mac (not sure why) but if your model is covered this is a better solution to reducing the volume than covering the speakers with your hands.