I work with modeling a number of aqueous solutions, but mostly it boils down to single-component saline solutions. The industry standard for determining various saline solution quantities such as conductivity, activity, and density as a function of salinity and temperature is OLI.
OLI also provides capabilities that are way over the top for what I'm looking for (e.g. corrosion, scaling), and I'm wondering if an alternative exists that is less capable and hopefully less costly.
I have experience with writing and compiling software, so user-friendliness is not that important for me.