The application is built using Ruby on Rails and the Vonage Video API to enable video watch parties with real-time chat functionality. The backend is written in Ruby, while the frontend is primarily client-side JavaScript. The code is organized into separate files for different concerns, such as app_helpers.js, chat.js, party.js, and screenshare.js. These classes are then instantiated in the opentok_video.js and opentok_screenshare.js files to create a functional video watch party application. The application also includes styling using CSS to make it visually appealing and accessible.