Mac: Often leave your Mac on at night, but forget to mute your system or turn the volume down? Silencer is a tiny menubar utility that can mute and unmute your Mac's speakers at a specific time every day.
Silencer will set you back $0.99 in the Mac App Store. The developer built the app because he had a cat that liked to curl up on his Macbook Pro at night (it was usually active rendering video or performing backups). If he forgot to mute the system, the first email he got in the middle of the night would wake the cat up -- and we all know what an irritated, rattled-awake cat will do in the middle of the night while you're sleeping.
Even if you don't have a cat, the app could be useful for keeping your system quiet without forcing you to turn it off, put it to sleep, or remembering to silence it.
Silencer [Mac App Store]