Recently a student I tutor was looking for an online graphing calculator. My brief internet search did not uncover anything satisfactory. But today I found one that really is good. It has only been available for a few months, and works on iPads too.
https://www.abettercalculator.com/
All written in HTML5/Javascript. Probably almost any application that was available ten years ago on any platform can now be ported to the web.