Computer modeling of biomolecules is aimed at studying the structure, dynamics and interactions of nucleic acids, proteins and cell membranes, examining the catalytic effect of enzymes, rational drug design etc. There is a whole range of methods - bioinformatics, classical molecular dynamic (MD) simulations, quantum-chemical ab initio calculations, or combined QM/MM approaches.
Among the software packages there is usually more or less full-featured freeware alternative.