It is an app where logged-in users can create chat rooms. You can add other users to these chat rooms and chat with them. Chat room and messaging features have been implemented thanks to the Socket.io. Chat rooms along with registered users are persisted in the Mongo DB except messages. I've used session cookies for authentication. Sessions are stored in the Redis DB. I've written unit tests for the service layer and the middlewares. I've also implemented the front end of the app to experience the Socket.io on the client.