Growl is a global notification system for the Mac OS X and Windows operating systems. Applications can use Growl to display small notifications about events which the user deems important, in a consistent manner. This allows users to fully control their notifications, application developers to spend little time creating notifications, and Growl developers to concentrate on the usability of notifications.
Growl includes bindings for developers who use the PHP, Objective-C, C, Perl, Python, Tcl, AppleScript, Java, and Ruby programming languages, and comes with multiple "display plugins," providing different styles for presenting the notifications.
The Growl Project website has a list of applications that support Growl, either inherently or through add-ons.
Plugins or scripts exist to add Growl notifications to iChat, Mail, Thunderbird, Safari, and iTunes (GrowlTunes).
(Growl for Windows,Mac Os X or Unix)