SocNetV - Social Network Visualizer (SocNetV) is a cross-platform, user-friendly free software application for social network analysis and...
Gephi - Gephi is an open-source software for visualizing and analyzing large networks graphs.
Graphviz - Graphviz is open source graph visualization software. It has several main graph layout programs.
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Centrifuge - Centrifuge is a complex and highly useful data analysis tool that allows for interactive data exploration.