Hey Mark! Wolfram|One and Mathematica both are implementations of Wolfram Language, so either would serve you perfectly for relearning calculus (make sure to check out our MOOCs!). The only material difference is that Wolfram|One comes stock with access to Wolfram Cloud, whereas Mathematica is by default a strictly local installation. The other differences are down to licensing/upgrades.

Thanks. I think that might be for a desktop perpetual license. I'd like cloud access and updates, so a yearly subscription is the only option for that (I believe).

What Wolfram products does this course use? Just Mathematica?

EDIT: I see it says "Mathematica" or "Wolfram One". I'm not clear on the difference. For a hobbyist trying to save money, is Mathematica a better option? I know you can get a cloud subscription to Mathematic How is that different from Wolfram One?