This application allows users to send and track faxes using the Twilio Fax API, built with Ruby and Sinatra. The application has a simple interface for uploading a PDF file and entering a fax number, which is then sent to the specified recipient via Twilio's API. The application tracks the status of the fax, including any errors that may occur during transmission. To protect the webhook endpoint from unauthorized access, the application uses Rack::TwilioWebhookAuthentication middleware. Once the fax has been sent, the user can view the status updates in real-time. The entire application is available to clone from GitHub and provides a working example of how to integrate Twilio's Fax API with Ruby and Sinatra.