free molecular modeling and molecular graphics tool

 BALLView provides fast OpenGL-based visualization of molecular structures,
 molecular mechanics methods (minimization, MD simulation using the
 AMBER, CHARMM, and MMFF94 force fields), calculation and visualization
 of electrostatic properties (FDPB) and molecular editing features.
 .
 BALLView can be considered a graphical user interface on the basis of
 BALL (Biochemical Algorithms Library) with a focus on the most common
 demands of protein chemists and biophysicists in particular. It is
 developed in the groups of Hans-Peter Lenhof (Saarland University,
 Saarbruecken, Germany) and Oliver Kohlbacher (University of Tuebingen,
 Germany). BALL is an application framework in C++ that has been
 specifically designed for rapid software development in Molecular
 Modeling and Computational Molecular Biology. It provides an extensive
 set of data structures as well as classes for Molecular Mechanics,
 advanced solvation methods, comparison and analysis of protein
 structures, file import/export, and visualization.