In the book I spend time with Gephi, which is a desktop application with versions available for Windows, OSX, and Linux, and is open source. For open source libraries, I discuss D3.js in the appendix but there are others, Sigma.js, arbor.js and cytoscape. I use KeyLines.js in many of the examples in the book, but that is a commercial library, not an open source one.
There are 29 Knuts in one Sickle, and 17 Sickles make up a Galleon. 42 tiny ads in a knut:
Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop