iWannaSleep is a timer application. You can set a countdown, after which iTunes is stopped or your computer is shut down or put to sleep. You can even specify a custom AppleScript to be executed when the countdown has reached zero.
Especially useful for having iTunes play some soft music before going to bed. If you don't want to switch off your computer manually (or you fell asleep already), it's good to know that "iWannaSleep" will care about that.
On top of that, by using a custom AppleScript, possibilities are almost endless. From a simple reminder function ("Don't forget to turn off the oven after 20 minutes") to complex tasks like making a backup!