Growl is a notification system for Mac OS X: it allows applications that support Growl to send you notifications.

Why use Growl?

• Control: Growl offers you complete control over which notifications are shown and how they are displayed. You will not receive any notifications that you do not want, because you can easily turn notifications (specific ones or all of them) off.
• Ease of use: When you start up a Growl-enabled application, it will "just work." Your apps can start displaying notifications right away.
• Consistency: Growl centralizes all your notification preferences into its preference pane - you can control them all from one place, and you know exactly how they are going to behave.
• Powerful: Growl is very flexible. Notifications can be emailed to you or spoken instead of displayed on the screen.

See supported applications.

Requirements:
OS X 10.5-10.6
Universal Binary

Also available are:
Universal Binary version 1.1.6 for OS X 10.4.11 +
Universal Binary version 0.7.6 for OS X 10.3.9