Windows: Whether you want to launch an application when your computer goes idle or you just want to make sure that your speakers are muted so email notifications don't annoy your coworkers when you're away from the office, System Silencer can help.
System Silencer has a set of stock toggles like turning off monitors, toggling sound and locking your workstation, all of which can be activated by your computer sitting idle for a specified number of minutes. You can fine tune the process by setting System Silencer to kill an active process or start a new one by launching an application. System Silencer can even be set to return things to their prior state when the computer is no longer idle — a very handy way to automatically turn the sound on and off, for example, based on whether you're using the computer.
Have a favourite application for tweaking settings on your computer? Let's hear about it in the comments.