Growl uses GNTP (Growl Notification Transport Protocol) to send notifications. GNTP is a MIME-like format.

Growl is a global notification system for Mac OS X. Any application can send a notification to Growl, which will display an attractive message on your screen. Growl currently works with a growing number of applications.

Notifications are a way for your applications to provide you with new information, without you having to switch from the application you’re already in.

Growl uses on all platforms the basic UDP (User Datagram Protocol) to send notifications. UDP is a binary format.