REFPROP is a software program for the prediction of thermophysical properties of fluids, developed by the National Institute of Standards and Technology (NIST).
For most pure fluids, the equation of state is obtained by fitting an expression for the Helmholtz free energy to experimental data.
[1] REFPROP also predicts surface tension, viscosity, and thermal conductivity for many fluids, either using extended corresponding states formulations or fluid-specific equations fit directly to experimental data.
The full list of fluids properties implemented in REFPROP v10.0 can be found in Table 2 of Huber, et al.
[1] REFPROP v10.0 implements equation of state models for 147 pure fluids, listed in Table 1.