This project provides a Fortran code for simulating the mechanics and energetics of human walking in three dimensions. The model has 23 degrees of freedom (pelvis, trunk, thighs, shanks, feet, toes) and 40 Hill-based muscle model actuators. The muscle excitation control scheme is customizable. Implementations of several popular muscle energetics models are provided. Experimental joint motion and GRF data are provided for performing tracking simulations. The model can also perform predictive simulations (no tracking) through customization of the cost function.