WCF

Windows Communication Foundation (formerly code-named "Indigo") is a set of .NET technologies for building and running connected systems. It is a new breed of communications infrastructure built around the Web services architecture. Advanced Web services support in Windows Communication Foundation provides secure, reliable, and transacted messaging along with interoperability. The service-oriented programming model of Windows Communication Foundation is built on the Microsoft .NET Framework and simplifies development of connected systems. Windows Communication Foundation unifies a broad array of distributed systems capabilities in a composable and extensible architecture, spanning transports, security systems, messaging patterns, encodings, network topologies, and hosting models. Windows Communication Foundation is available for Windows Vista™ as well as for Windows XP and Windows Server 2003

More Info http://msdn2.microsoft.com/en-us/library/ms731082.aspx