Yahoo Pipes can export a JSON definition of the blocks used to construct a particular pipe, and how they are wired together.... which means it's possible to user Yahoo Pipes as a visual design environment and export the JSON definition of a pipe, then compile it and run it elsewhere.
I don't know if there is a .NET implementation, but there is a Python compiler, pipe2py, that will create a Python equivalent of a Yahoo pipe and allow you to run it elsewhere. See also Exporting Yahoo Pipe Definitions, Compiling Them to Python, and Running Them in Scraperwiki, which describes how to compile Python equivalents of Yahoo Pipes in Scraperwiki.