Computer music: a bastion of interactive visual dataflow languages

Max/MSP is commercial/proprietary ; Pd ( http://en.wikipedia.org/wiki/Pure_Data ) is a BSD-licensed alternative (Miller Puckette is the original author of both).

In the commercial arena, see also Reaktor ( http://en.wikipedia.org/wiki/Reaktor ).

I loved how Steele ridiculed visual programming in his "50 on 50" talk* by showing Piet † as exemplary for the paradigm.

* http://lambda-the-ultimate.org/node/3101

† http://en.wikipedia.org/wiki/Piet_(programming_language)

I think it's pretty safe to say that dataflow is one of the most severely underused programming paradigms today.

(I'm not fond of "visual" programming however, except where it opens new possibilities to someone who would never dream of programming the "real" way).

Ptolemy is an academic project work looking at. From this perspective, its an attempt to incorporate some of the advantages of 'real' programming into a visual environment. http://ptolemy.eecs.berkeley.edu/ptolemyII/ptIIlatest/