Many dataflow-oriented frameworks have a visual programming environment. Examples are MAX/MSP and LabVIEW. Also, the VTK Designer has recently introduced a similar environment for C++ (and VTK), based on the Generic Component Framework and is released under the GNU GPL license.

I have started a small example GUI dataflow editor built on top of the Dataflow.Blueprint layer, showing that the Dataflow library is an adequate basis for such a visual programming environment. This will be developed more in time. In particular, I'm interested in