The collection of programs called nauty, written by Brendan McKay, computes automorphism groups of graphs and digraphs. It is available at http://cs.anu.edu.au/~bdm/nauty. The package Nauty is an interface to it.
It is distributed with the following copyright notice: Copyright (1984-2010) Brendan McKay. All rights reserved. Permission is hereby given for use and/or distribution with the exception of sale for profit or application with nontrivial military significance. You must not remove this copyright notice, and you must document any changes that you make to this program. This software is subject to this copyright only, irrespective of any copyright attached to any package of which this is a part. Absolutely no guarantees or warranties are made concerning the suitability, correctness, or any other aspect of this program. Any use is at your own risk.