The author, Sam Agnew, built a notification system that allows users to receive SMS notifications whenever the International Space Station (ISS) flies over their location. The system uses Python, Redis-Queue, and Twilio's Copilot features to schedule tasks and send text messages. The application has a web interface where users can enter their phone number and latitude/longitude, and then subscribe to ISS notifications. The system also includes Geo-Match and Sticky Sender features, which enable the use of a pool of Twilio numbers for international subscribers. The author provides step-by-step instructions on how to build and deploy the application using Flask and Redis-Queue.