Tessel

Tessel is a 3D "compiler" to produce crystal and molecular models, parametric surfaces and several forms of sphere tesselations. Molecular models combine balls-and-sticks, arrows and coordination polyhedra representations of pure and defective crystals, finite molecules or clusters. The Madelung potential of an ionic system can be computed and depicted on an arbitrary plane or surface. The common crystallographic cell (parallepipedic), as well as the Wigner-Seitz cell or the irreducible components of the WS cell can be easily added to the plot.
Find Tessel at: http://azufre.quimica.uniovi.es/src/tessel/examples/tessel2b.html