The graphing program I used is Graphviz, from here. On the laptop I'm using, I have Graphviz.app (2.20), which was installed about 2 years ago, but they are currently up to version 2.26, and 2.27 is in development. The Mac OS X .app version seems to not be upgraded anymore, but my copy still works. You can also get Graphviz from MacPorts.
I can launch the command line version like so (or whatever the path to the MacPorts version is):
but I normally double-click (or just drop a file with commands on top of the application icon). A very simple example gives the graphic above:
Graphviz does the heavy lifting for us. I like that!
Code for the example from last time: