ASP.NET SignalR is a is a new library for ASP.NET developers that makes it incredibly simple to add real-time web functionality to your applications. What is "real-time web" functionality? It's the ability to have your server-side code push content to the connected clients as it happens, in real-time.
This project is part of ASP.NET vNext. You can find samples, documentation and getting started instructions for ASP.NET vNext at the Home repo.