Ask HN: What tools do you use to solve practical math problems?

I find myself regularly needing to solve different types of math problems. Nowadays there's a number of powerful tools, and I've dabbled with many of them. I want to choose a set of tools and stick with them long-term so that I can become more familiar with the tools and thus more productive.

I'm being deliberately vague about what kinds of problems since others might find the information useful even if I do not.

Which tools do you use? What do you use them for? What do you like about them? What do you dislike?

Inexhaustive list of popular maths tools:

Languages: - Python - Julia - R - Lisps

Integrated Math Packages: - Mathematica - Maple - Matlab - GNU Octave - Maxima - Mathcad - Anaconda - SageMath

Notebooks: - Jupyter - Emacs/Sublime/VSCode/etc. IPython Notebook

Cloud: - CoCalc (formerly SageMath Cloud) - Wolfram Alpha / Cloud - Desmos

Calculators: - TI - HP - Emacs calc - bc

Don't Forget: - Pencil and paper