Have you ever tried Qalculate? I don't see it mentioned in your article. It feels like it addresses most of your points for creating Chalk, and it's already cross-platform.
Most people didn't understand that my goal was not to benchmark all existing calculator apps. It is on purpose that I did not mention all "pretty good" softwares, because I cannot know them all.
The article I wrote wants to mention every point that should be adressed (in my opinion) to make a good calculator.
Qalculate, like many others, does address some of them.
But as far as I know, only Chalk addresses all of them.