Tons of different things: https://www.sympy.org/en/features.html. Try it for yourself: https://live.sympy.org/

E.g. find critical points on a surface:

  e = (x-y+2)*(x**2+y**2-9)
  solve([e.diff(x), e.diff(y)], [x, y])

Note that this online demo runs at a restricted speed; locally (e.g. install Anaconda and use Jupyter Notebook or QtConsole) it's much faster.