Messenger Apps are a new feature in Intercom Messenger that allows businesses to integrate third-party apps and tools into their workflow, making it extremely customizable. To simplify app development, ngrok is a useful tool that creates public URLs exposing a web server on a development machine, allowing developers to set webhook URLs while developing their app without additional infrastructure. With ngrok, developers can get started quickly by downloading the tool and setting up a tunnel to their server, which exposes their development server to the outside world. The ngrok web interface provides useful features such as inspecting traffic, replaying requests, and request/response validation, making it an invaluable tool for building Messenger Apps.