gSpan is a software package of mining frequent graphs in a graph database. Given a collection of graphs and a minimum support threshold, gSpan is able to find all of the subgraphs whose frequency is above the threshold. The details of gSpan can be found in the following papers,
gSpan: Frequent Graph Mining Package. (binary code, updated in Feb, 2009), 64-bit binary(linux).
The C++ source code for gSpan is available at gBoost.
The Java source code for gSpan is available at ParSeMiS - the Parallel and Sequential Mining Suite.
The C++ source code for Gaston (another frequent graph pattern mining) is available at Graph/Sequence
/Tree extractiON Tool.