Limited
An uninviting interface with little appeal, except that it's free and has no advertising. Hmm, actually, I'm going to add a star for that! The flat colour is not a problem but I don't get why the operands do not have the standard appearance. What's wrong with the simple x / + - ? Even if intended to educate someone unfamiliar with RPN, surely it's unnecessary to have these keys denoted as y+x, etc.? I'm giving two stars for the fact that it has no advertising and is free. That much is to be commended; but please rethink the interface.
