Ruby on Rails is used to send SMS (Short Message Service) alerts to a list of system administrators if something goes wrong on the server. The application uses the Twilio REST API to send messages. A YAML file is used to store the phone numbers of the administrators. The `rescue_from` method is used to rescue any exception raised in controller actions and trigger SMS alerts when something goes wrong. Custom alert messages can be created using a template, and images can be included with the message for US and Canadian phone numbers. The application also includes features such as sending reminders and reducing no-shows.