Pajek is a computer program for the analysis and visualisation of graphs. It was written by Vladimir Batagelj and Andrej Mrvar of the University of Ljubjana can be downloaded from http://pajek.imfm.si/doku.php.
Batagelj, V. and Mrvar, A. (2006). Pajek. Program for Analysis and Visualization of Large Networks. Reference Manual, version 1.15. Ljubljana.