SignalR
Incredibly simple real-time web for .NET
... dependency injection, authentication, authorization, and scalability. While chat is often used as an example, you can do a whole lot more. Any time a user refreshes a web page to see new data, or the page implements Ajax long polling to retrieve new data, it's candidate for using SignalR. SignalR also enables completely new types of applications that require high-frequency updates from the server, such as real-time gaming.