Gephi is developed in an international open source consortium to enable easy visualization and analysis of network graphs. It is a very versatile tool that can be used to explore any type of graph. At the TANT-Lab we use Gephi routinely both in class, for teaching our students the visual network analysis, and in various research projects.
Below is a video of one of our own web corpora - more than 2000 Scandinavian food sites connected by their hyperlinks - being spatialized with the ForceAtlas2 layout algorithm in Gephi. As the spatialization of the graph progresses, you will see clusters of closely interconnected sites becoming visually discernible. At 00:11 the nodes are sized by their in-degree, i.e. the sites are attributed importance according to how many links they receive from other sites in the network.