Improving upon the design of a calculator app is incredibly difficult. And before people complain that it's not improved, yes it is. For most people, this is way better. Congrats to him, he's living the dream. Building software that does a job, and then getting paid for that software. I just hope he doesn't suffer too many copycat apps.
This article made me realise why I use a python shell over a calculator app. It's nice to refer back to my previous computations and results. Several people here mention RPN; I work in tech, definitely understand stacks and get that I would be able to view my previous computations. Yet it's not something I took the time to discover, there were always other ways.
I've always believed that there is still a lot of low-hanging fruit left in crafting user friendly experiences for consumer facing applications. Who would have guessed this would be the case even in the design space of something as fundamental as calculators! ~20k paid users seems surprisingly large. But I'm not plugged into the app dev scene, so perhaps this isn't unusual.
> I just hope he doesn't suffer too many copycat apps.
There were 2k clones of flappy bird within a month of its release. By now there must be at least a dozen programmers copying this idea (Twin-Calc) for other platforms, myself included.
