Joerg Wegner mentioned in his blog the graph mining program ParMol which integrates four mining algorithms: MoSS (aka MoFa) and Gaston, which I mentioned in November last year , and FFSM and gSpan, which I did not know about yet. ParMol provides a common interface to the four different algorithms and is, like the four mining modules, licensed GPL. An interesting aspect is that Gaston was originally written in C++.