A general-purpose, object oriented software system has been developed for the simulation and dosimetric analysis of brachytherapy applications. The flexible object-oriented design makes this system very versatile, offering the possibility to configure it for different types of brachytherapy techniques (such as I-125 or Ir-192, for instance). The dosimetric system is based on the Geant4 Simulation Toolkit, allowing accurate geometry and material description and precise particle transport, down to low energies. These characteristics allow to simulate accurately effects such as the source anisotropy, and to calculate accurate dose distributions. The Geant4 Toolkit also gives access to various visualization systems, accessible through a variety of drivers, and, thanks to the object-oriented technology, allows an easy interface to powerful modern analysis system for dosimetric calculations. The accuracy of this Monte Carlo based dosimetric system has been verified through comparison with experimental data, concerning various brachytherapic sources and applicators: a selection of experimental validation results is presented. The dosimetric system is parallelized, to achieve fast computational results (dose distributions, isodose curves etc.), suitable to usage in clinical practice. The advanced technique adopted for parallelization allows transparent access either to a local computing farm, or to a geographically distributed computing GRID.