NodeXL is a free, open source tool for generating and exploring network graphs from Microsoft Excel files. It is particularly suited to data from social media sources, and includes the ability to directly import data from Twitter, YouTube, Flickr and email, with additional plugins available for gathering data from Facebook, Microsoft Exchange, wikis and URLs. The tool generates visualizations that can be adjusted, zoomed and filtered, with additional features for vertex grouping, graphing metric calculations, and automating tasks. NodeXL can both import and export data in GraphML, Pajek, UCINet and matrix formats.

From the website: NodeXL is a free, open-source template for Microsoft® Excel® 2007 and 2010 that makes it easy to explore network graphs. With NodeXL, you can enter a network edge list in a worksheet, click a button and see your graph, all in the familiar environment of the Excel window. (http://nodexl.codeplex.com/)

The book Analyzing Social Media Networks with NodeXL: Insights from a Connected World is the most comprehensive source on NodeXL. Accompanying slides and datasets are available on the NodeXL Teaching Resources page. (http://nodexl.codeplex.com/documentation)