I was sent email by Alastair McKeeman from Connective Logic Systems, a UK based company.
They've done some cool work on tools to build concurrent apps targeted at multi-core processors. They have a graphical designer hosted in Visual Studio, implemented using DSL Tools. Take a look at http://www.connectivelogic.co.uk/toolset.html which contains a screenshot. They've also built graphical analysers and debuggers.