When I saw the headline, I wondered what was so special about this. But actually reading the description, the UI sounds like a significant improvement in usability, such that I might actually consider using a postfix calculator like this.<p>On a side note, the description of arithmetic says that - and / swap the inputs, and it describes the operators as popping values a and b (and in the case of swap, then pushing a and b back on). This is a little confusing. It would be much simpler just to say that all binary operators pop values b and a. Now you don't have to swap anything, because - and / will still just perform a - b and a / b. And the fact that this swaps + and * is irrelevant, because those operators are commutative. And the swap operator makes more sense, because it "pops values b and a, and pushes values a and b", so you can now actually see the swapped values in the description.