Wow, ran across these just now. Very cool!

StumbleUpon Alerter

StumbleUpon Alerter is a small tool that sits in the system tray. It keeps an eye on all of your discoveries on StumbleUpon and plays a noise whenever someone reviews or gives your sites a thumbs up. Open the main window to view information about each discovery - including a list of people who have reviewed, thumbed up or thumbed down your sites. More details »

Digg Alerter

Used by some of the influential Digg users. Digg Alerter is a program that sits in your system tray and plays a little noise whenever your submissions are “Dugg”. You can also click on a submission to view a list of people who have dugg and commented on your articles. Click here for more details »

Creators:  http://blog.adamant.com.au/