Qalculate! is a multi-purpose cross-platform desktop calculator. It is simple to use but provides power and versatility normally reserved for complicated math packages, as well as useful tools for everyday needs (such as currency conversion and percent calculation).
Just to mention it…libqalculate also comes with CLI
qalctool which I use all the time, it’s a great calculator. And Plasma’s krunner uses libqalculate as back-end for their integrated calculator. I think anything that contains a “=” in krunner get send to libqalculate allowing things like=plot(x^2+2x-3 ; -10)in the krunner input.Edit: The function list is something worth having always a hand when doing calculations with krunner.