For the graphical part, we use the very nice Visual Toolkit library (vtk). See the links at our homepage.
For actually using vtk, you need a wrapper (a program that calls vtk routines). The wrapper of vtn is, with kind permission, based on the Melati wrapper for vtk by Jos Runarko at the 'Forschungszentrum Strangpressen' in Berlin. See the links at our homepage for Melati.