NodeXL includes a separate program called the NodeXL Network Server. This is a command-line program that can be used to download Twitter networks on a periodic basis—a twice-daily download of the network of people who tweeted a specified hashtag, for example—and store the graph data in GraphML files or NodeXL workbooks. It's an alternative to manually using the Twitter import features built into the NodeXL workbook, and it's ideal for researchers who wish to observe how Twitter networks change over time.
The NodeXL Network Server is meant for use by people with moderate system administration skills. It is not difficult to use, but it is not intended for the same audience as the NodeXL workbook, where ease of use is of high priority.