I made a project ("lunchbus") to play with Spring Boot + websockets + AngularJS 1.5 + Groovy + Redis. This may be interesting to those who are interested to see how these are set up. The project also has the configuration to run on Heroku.
The lunchbus app keeps track of who owes lunches and to whom, a list of people and places that can be selected, a button to randomly select a place, a chat functionality, and a demonstration of high-speed log output from backend. Persistence is provided by Redis. Due to how it uses Redis, it's just almost ready for horizontal scaling with multiple servers, for that time that you have over 100,000 people going to lunch with you. All that's needed for that is to integrate Spring Boot to Redis pubsub.
My goal is to learn Spring Boot and websockets primarily, and also to see what does an application relying solely on websockets look like and its strengths/weaknesses.