NIST does not sell the software directly to end-users. Instead, they license it to distributors.
Improved compatibility for Mac users via a new shared library, enabling use with Python or Excel 2011. Installation and Setup REFPROP | NIST refprop 10 download
Many users use REFPROP as an Excel Add-in. Here is how to set it up: NIST does not sell the software directly to end-users
Here is your step-by-step guide to legally downloading, installing, and getting started with REFPROP 10. and getting started with REFPROP 10.