The traditional stateless design for web apps can become increasingly troublesome with new classes of web apps and increasing end-user expectations. This traditional approach, where the web application is essentially a stateless front-end and all state is written/read to a database, falls short when we have ever-increasing workloads and requirements for highly responsive, near real-time systems. Add in the requirements for concurrency management, scalability and fault-tolerance, and the traditional approach becomes even less attractive. By combining the features of the Actor Model (Akka.NET) with the capabilities of SignalR and a front-end SPA library, we can more easily create next-generation reactive, stateful, and concurrent SPA web apps. In this course, we'll be using the example of multi-player online games, as these are a great example of reactive concurrency in action.