M-x calc in Emacs is really capable and fun even.
“Calc” is an advanced calculator and mathematical tool that runs as part
of the GNU Emacs environment. Very roughly based on the HP-28/48 series
of calculators, its many features include:
• Choice of algebraic or Reverse Polish notation (RPN), i.e.
stack-based, entry of calculations.
• Arbitrary precision integers and floating-point numbers.
• Arithmetic on rational numbers, complex numbers (rectangular and
polar), error forms with standard deviations, open and closed
intervals, vectors and matrices, dates and times, infinities, sets,
quantities with units, and algebraic formulas.