This is the I3RC community Monte Carlo model for solving problems in radiative transfer in three-dimensionally variable atmospheres. The basic framework is a set of modules that describe parts of a radiative transfer problem, such as the illumination source or the three-dimensional distribution of optical properties within a domain. On top of this framework we have built a solver capable of computing fluxes and intensities at the top and bottom boundaries of a domain and flux divergence within the domain. We have also provided a general purpose driver, programs to help define problems and do preliminary calculations (i.e. the calculation of cloud optical properties), and several example programs.