The document discusses the evolution of a Catalyst application to use lighter weight components including removing the model layer and using Redis for sessions and RabbitMQ for the backend. It started as a standard Catalyst app and was stripped down over time, moving content to CouchDB, sessions to Redis, and the backend to RabbitMQ. Lessons learned included using plugins, choosing technologies like Redis, CouchDB and RabbitMQ, and getting a minimum viable product out quickly before refactoring.