GNU Units unit conversions
Also, look at this awesome example of what Units can do (It is a calculation of the effect of adding salt to a quantity of water on the boiling point of the resultant solution, with the answer in Δt in degrees Fahrenheit)
For freezing-point depression, consult this formula.
Now with slightly modified unit definitions! The only difference is that I
added a dummy primitive unit "unit" (abbr. "u") to assist in cases where the
unit you want either doesn't exist or doesn't matter.
Currency exchange rates are fairly out of date (2018-10) so I recommend not relying on those. Try literally any other service for that if you need accurate rates.