GitHub is a large community where coders can collaborate on software development projects. People check code in and out, make edits, etc. Franck Cuny maps this community (with Gephi), based on information in thousands of user profiles.
Cuny then looks at the structure within the coding networks, which is the most interesting part of the project. The Python map, for example, shows several projects, with Django in the dominant center.
In contrast, the PHP map is a lot more segregated.
I do wish there were some labels for the clusters so that I knew what exactly I was looking at, but if you like, you can download the the files (bottom of post) and explore them in Gephi yourself. See the rest of the graphs over on Flickr.