PFLOTRAN is an open source, state-of-the-art massively parallel subsurface flow and reactive transport code. The code is developed under a GNU LGPL license allowing for third parties to interface proprietary software with the code, however any modifications to the code itself must be documented and remain open source. PFLOTRAN is written in object oriented, free formatted Fortran 2003. The choice of Fortran over C/C++ was based primarily on the need to enlist and preserve tight collaboration with experienced domain scientists, without which PFLOTRAN's sophisticated process models would not exist.
PFLOTRAN employs parallelization through domain decomposition using the MPI-based PETSc framework with pflotran-dev tracking the developer version of PETSc (i.e. petsc-dev) available through Bitbucket.
Current build status for pflotran-dev.
Interesting link on modern Fortran
Questions regarding PFLOTRAN installation (i.e. not answered by the FAQ) and bug reports: pflotran-dev at googlegroups dot com
Questions regarding running PFLOTRAN: pflotran-users at googlegroups dot com