igraph is one of the most popular libraries for graph analysis and manipulation. Written in C/C++ and available also for Python and R, the library is very popular amongs academics because it greatly speeds up experiments, exploratory analysis of networks, and helps visualizing networks efficiently. Key features of igraph include generators for a wide variety of network models, algorithms for computing centrality measures, ease of integration with high-level programming languages, and portability. Of course, igraph is a free software as well.
R/igraph will be presented by Katherine Ognyanova. Katya is an Assistant Professor at the School of Communication and Information, Rutgers University. She does work in the areas of computational social science and network analysis. Prior to her appointment at Rutgers, Katya was a postdoctoral researcher at the Lazer Lab, Northeastern University and a fellow at the Institute for Quantitative Social Science, Harvard University.