The graph above shows an example of a difference chart used as an example in the book D3 Tips and Tricks. It is based on the simple difference chart example here.
The graph shows the difference in the number of daily downloads between R Programming for Data Science by Roger Peng and The Elements of Data Analytic Style by Jeff Leek. The respective books can be found as links from the legend or the appropriate graph area.
There is an explanation of the code available in D3 Tips and Tricks