The author created a simple Rails app that uses the Twilio gem to send SMS notifications to users who subscribe to receive cat facts. The app allows users to subscribe by texting "SUBSCRIBE" and unsubscribes by texting "UNSUBSCRIBE". When a new cat fact is added, all subscribers are notified via SMS with the latest fact. The author built this app as a way to deal with Alternate Side Parking rules in NYC and shares it as an example of how developers can use Twilio to create simple apps that interact with users through text messaging.