Growl 2.0

Growl lets you know when things happen. Files finished downloading, friends came online, new email has arrived - Growl can let you know when any event occurs with a subtle notification. The rest of the time, Growl stays out of your way.
Along with letting you know when things happen, Growl also gives you full control over how you are notified and what action (if any) you want to take in response