The Emacs Wiki does describe it as the "poor man's Mathematica". Org-tables with Calc functions are also quite nice.
That's neat. I had no idea calc could do calculus!
It can indeed! Adapting the first example from the article, in Emacs type:
M-x quick-calc RET
integ(exp(-x^2),x) RET
You'll see that it immediately responds back with: erf(x) sqrt(pi) / 2I always facepalm when I do math outside of Emacs. Calc was never really advertised, it's not a toy.
Also I've heard it might be scraped from vanilla emacs and made into an extesion, but I may be confused.
I use it quite heavily since it's right there in my editor. It's kind of like a good-enough phone camera that's always close at hand vs. a dedicated camera that's better but takes more effort to have ready.