Growl is a notification system designed for macOS that allows applications to send alerts to users in a visually appealing way. It provides a consistent interface for notifications, making it easier for users to manage and respond to alerts from different applications. Developed by Evan Schoenberg and released in 2005, Growl supports various types of notifications, including messages, reminders, and updates. Users can customize the appearance and behavior of notifications, choosing from different themes and settings to suit their preferences.