Hexadecapole is a small business dedicated to the maintenance and further development of ereg, an open source software package for modeling of proteins and nucleic acids. Functionality provided by ereg includes structure prediction, sequence design of thermodynamic stability, homology model building, and calculation of pKa for ionizable groups. Enabling this functionality are an accurate potential energy function and algorithms for accomplishing efficient global minimization within subspaces of torsion angle degrees of freedom.