It allows you to simply drag and drop dependent variables in multiple formulas to quickly translate real world problems into actual numbers. For example: If I buy amount x of y I can create z which can be sold for $a each. How much do I need to sell to make $b total?
Is there anything like this for mac or linux?
The tool you linked to has an intuitive UI and is useful for simple calculations. I can see it being useful for every day use for folks who aren't that savvy with computers or math.
Spreadsheets however are a more much general tool (and only marginally more complex) that will let you do those calculations, but scale those calculations to much more complex models with almost no added complexity.
I have seen some really mindboggling things done with spreadsheets (and have done such things myself). But I can as effortlessly whip up the calculations on the demo page in almost the same amount of time.
I would say for most people, it would be a better investment of time to learn how to use a spreadsheet.
It could handle at least moderately complex systems of equations: I entered all the formulae for the algorithm of Oudin (used to calculate the date of Easter), and it traversed all the equations to reach a correct result. I'd still love to have something like that today, without paying $200! Sadly, I don't think it was open source.
For simulations, computational geometry, computational probability. I prefer Golang scripts. You can subdivide computation using goroutine workers. And it's blazingly fast
That said, there is literally no downside to gaining some proficiency with professional tools: Sage / Octave, Matlab, Mathematica, SciPy