I installed the Graphviz GUI from pizelmap.com, but it appears to only be a viewer for .dot Graphviz files. I am looking for a graphical editor, where I can create diagrams by pointing and clicking--just like the iPhone app Instaviz.
I would rather not code graphs by hand.
Does anyone know of anything--preferably free?
Have you looked at the Mac port of Graphviz from the same people who do Instaviz? Otherwise, a not cost-free option is OmniGraffle which has been the graphical editor of choice on OS X for years; it uses Graphviz under the covers and understands .dot files. If you want to go hard-core, there's a port of the basic AT&T graphviz and some language wrappers available through MacPorts.