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.