CoolProp is an open-source, cross-platform, free property database based in C++ that includes pure fluids, pseudo-pure fluids, and humid air properties.
To get CoolProp head to how to get it
To see how simple this is, go to the examples
The changelog is here
As of May, 2013, 107 pure and pseudo-pure fluids are included
Ian Bell , University of Liege, Liege, Belgium
Sylvain Quoilin , University of Liege, Liege, Belgium
Jorrit Wronski , Danish Technical University, Copenhagen, Denmark