igraph is a library for creating and manipulating graphs. It is intended to be as powerful (ie. fast) as possible to enable the analysis of large graphs.
See http://igraph.org for installation instructions, and documentation.
Igraph can also be used from R, see https://github.com/igraph/rigraph, and from Python, see https://github.com/igraph/python-igraph