It goes "ding" when there's stuff.

Well, somewhat. Actually, it lights up. I'm referring to the blink(1), which technically is just an LED you plug into a USB port. But that's the beauty of it. When does it light up? Whenever you want it to. If you know how to make a program track it, you can make a blink(1) respond to it. To start they have a few demo applications, picking a color for it, making it flash to music, but it also includes a program that just tells a blink(1) "light up like this" as well as code for using it in Java and C. Already included is a program that will light up whenever a phrase is matched on Twitter, and the concept could be easily applied to something else, both with full programs and with little scripts. The blink(1) is available for preorder from ThingM here.