"Polyphonic C# extends the C# programming language with new asynchronous concurrency abstractions, based on the JoinCalculus. The language presents a simple and powerful model of concurrency which is applicable both to multithreaded applications running on a single machine and to the orchestration of asynchronous, event-based applications communicating over a wide area network."
http://research.microsoft.com/%7Enick/polyphony/
Has now been merged with MicrosoftXen and renamed Cw [CeeOmega].
See CsharpLanguage, JoinCalculus, PiCalculus, CarHoare, CommunicatingSequentialProcesses.