(author here) The graphs are stock graphviz output, the linear layout is called "dot" (the default), and the nebulous layout is "sfdp". For your googling pleasu

(author here) The graphs are stock graphviz output, the linear layout is called "dot" (the default), and the nebulous layout is "sfdp". For your googling pleasure it's a "force directed graph layout", and there are many libraries to assist with it. d3.js has a force layout built in, for instance.