REFPROP 10 comes with a REFPROP.dll file that allows other programming languages to call the thermodynamic routines.
NIST REFPROP (Reference Fluid Thermodynamic and Transport Properties) is the gold standard software for calculating the thermophysical properties of pure fluids and fluid mixtures. Version 10 introduced significant updates, including new equations of state and mixture models. refprop 10 download
New reference equations of state for ammonia, helium, and heavy water, plus several new refrigerants like R1233zd(E) and R1336mzz(Z). REFPROP 10 comes with a REFPROP