ParaDiS is a free large scale dislocation dynamics simulation code to study the fundamental mechanisms of plasticity. It was originally developed at the Lawrence Livermore National Laboratory. It is written in C (with a little C++) and uses the MPI library for communication between processors. It runs routinely on 100-1000 processors and scalability on 132,000 processors of BlueGene/L has been demonstrated.
This site contains the information about how to use the code and the procedure on how to obtain a free copy of ParaDiS.