The Courier Designer tool allows users to create, modify, and test notification templates seamlessly, regardless of their technical expertise. The AI content generator, a GPT-3 model-based tool, optimizes messaging for each channel and can even create new notifications from scratch, all free to use with all plans. This feature, combined with the changelog feature, enables teams to view changes in granular detail before publishing, providing a more transparent workflow and control over different versions of the code. The Designer allows users to adapt templates to suit various channels, including email, SMS, WhatsApp, Discord, and Slack, making it easy to manage notifications across multiple platforms.