We had this in the early 1990's, it was called Mathematica [0]
[0] - https://writings.stephenwolfram.com/2013/06/there-was-a-time...
It was eye-wateringly expensive and required a high-end system, though. It was good, and I liked it too, but it's not the same as being usable from pretty much anywhere for $0.
Not just running right there and re-rendering in the browser you didn't.
We got alone fine for decades without browsers.
Mathematicians used to send each other letters in the mail until very recently. Perhaps I do not understand what you mean?
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Great tool. Reminds me of Instacalc, which has bee around forever.
This is pretty cool, I have a long running hobby project to make something similar in the terminal. https://github.com/ShaneMarusczak/rm-repl