Looks very cool, congratulations! Have you tried Emacs Calc? Chalk reminds me of Emacs Calc, but without the symbolic computation (and without date calculations or anonymous functions).
I don't use Emacs, but I feel that people should just have access to a decent calculator without digging developer forums.
As good as Emacs Calc is, we can admit that it's unlikely to be seen as an easy-to-find lightweight tool.
I'm not sure what you mean by "digging developer forums", but I fully agree with you that Emacs Calc is not a good choice for everyone, in fact, I would not recommend it to anyone that isn't already an Emacs user (but for people who are already Emacs users I do highly recommend it, since it has a ton of functionality and is an easy-to-find lightweight tool ---if you're already in Emacs anyway).
I was just curious to see if you had tried it, since it seems similar in spirit to your project, and thought you might be able to borrow some ideas from it.