Q is a molecular dynamics (MD) simulation package which, unlike other MD codes, has specialized since its conception (Marelius et al. 1998) on three specific types of free energy calculations. These calculations are based on the methods: empirical valence bond (EVB), free energy perturbation (FEP), and linear interaction energy (LIE). The program is similar to GROMACS in being force-field agnostic, meaning that it provides no force-field, but can rather use common force-fields such as CHARMM, AMBER, OPLS, and GROMOS.