Voro++ is a software library for carrying out three-dimensional computations
of the Voronoi tessellation. A distinguishing feature of the Voro++ library is
that it carries out cell-based calculations, computing the Voronoi cell for
each particle individually. It is particularly well-suited for applications
that rely on cell-based statistics, where features of Voronoi cells (eg.
volume, centroid, number of faces) can be used to analyze a system of
particles.

WWW: http://math.lbl.gov/voro++/