Courier is a notification service that centralizes all of your templates and messaging channels in one place, increasing visibility and reducing engineering time. It allows developers to send important alerts from their web or mobile app via SMS, email, Slack messages, push notifications, or other messaging channels. Courier provides automation logic around notifications, enabling developers to avoid bombarding users with excessive messages. The service offers multiple notification channels, including SMS, email, Slack, MS Teams, and push notifications. It also features a no-code designer for automations, which can be invoked via the Courier Automations API. This allows users to abstract complex workflows into templates using drag-and-drop components. Courier integrates with popular platforms like Segment, Twilio, and Segment, making it easy to implement in-app notifications for web and mobile applications. The service offers a free tier with 10,000 monthly notifications, allowing developers to get started immediately.