This is a directed graph visualization based on data collected from the Netscan project at Microsoft research from Usenet newsgroup message traffic. In this image the dots are "nodes" representing authors or "posters" in a newsgroup about server operating systems for computers. The dots are connected by lines or "edges" representing the relationship "replied to".
The image highlights the variation in roles and social structure in newsgroups and other online discussion communities.
The C#UNG software that generated the image is freely available from research.microsoft.com. It comes with an Excel plug-in that allows users to generate their own network visualizations with any data they can get into a spreadsheet (that contains a properly formatted directed graph data structure). Your mileage may vary. Netscan can be found at netscan.research.microsoft.com.
Smith, Marc A., Researcher at Microsoft Corporation, 2007. Netscan: A Social Accounting Search Engine, Microsoft Research Community Technologies Group, netscan.research.microsoft.com