ASP.NET SignalR 
ASP.NET SignalR 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.
What can it be used for?
Pushing data from the server to the client (not just browser clients) has always been a tough problem. SignalR makes it dead easy and handles all the heavy lifting for you.
Documentation
See the documentation
Get it on NuGet!
Install-Package Microsoft.AspNet.SignalR
Get a sample on NuGet, straight into your app!
Install-Package Microsoft.AspNet.SignalR.Sample
LICENSE
Contributing
See the contribution guidelines
Building the source
git clone git@github.com:SignalR/SignalR.git (or https if you use https)
Windows
After cloning the repository, run build.cmd.
NOTE: Opening the solution requires VS 2012.
Mono
After cloning the repository, run make.
Open Microsoft.AspNet.SignalR.Mono.sln to do development.
Continuous Integration
We have a CI Server (http://ci.signalr.net/)