SageMath is amazing: it is free and open-source!

From their website,

Mission: Creating a viable free open source alternative to Magma, Maple, Mathematica and Matlab.

which is really important. So I basically do everything on SageMath, and I wish I knew more mathematics to use it more, and more programming to help make it better.

Quick pro-tip: save your scripts as .sage files, and then run attach(filename) on a Sage REPL session, where filename is, well, your filename. It will instantly reload and run, which is great for debugging.

installing Jupyter Lab to have Sage notebooks