Pajek (Slovene word for Spider) is a program, for Windows, for analysis and visualization of large networks. It is freely available, for noncommercial use, at its download page. See also a reference manual for Pajek (in PDF). The development of Pajek is traced in its History.
Pajek is developed by Vladimir Batagelj and Andrej Mrvar. Some procedures were contributed also by Matjaž Zaveršnik.
A detailed introduction to Pajek is given in the book W. de Nooy, A. Mrvar, V. Batagelj: Exploratory Social Network Analysis with Pajek, CUP, 2005. Appendix 4. ESNA in Japanese, TDU, 2010.
For a short description see Batagelj V., Mrvar A.: Pajek - Analysis and Visualization of Large Networks. in Jünger, M., Mutzel, P., (Eds.) Graph Drawing Software. Springer, Berlin 2003. p. 77-103.
An improved version of the paper Batagelj V., Mrvar A.: Pajek - Program for Large Network Analysis, presented at Sunbelt'97, was published in Connections 21(1998)2, 47-57 - (preprint Prison Kinemage).