...send music from iTunes to your external speakers and keep the annoying beeps and blips of iChat going through your computer's built-in speaker.
...mute any application's sounds all together.
...change the volume of some applications relative to others. Make your email client's alerts quieter, and you'll never again be jarred from work just to receive spam.
What's new in this version:
Detour has been retired from active development. It is now freely available and will automatically register itself, enabling unlimited use.