Its name is Numerical and it is an iOS app developed by Andrew J Clark, with a focus on design and user experience. The slogan of Numerical, The Calculator Without Equal, talks already about one of its main functionalities.
It is mainly about the experience. Everything is fluid and the buttons are reduced to the minimum necessary. The color of the buttons fades whenever they are disabled and the whole interface seems an obvious solution.
The history automatically stores previous calculations. Swipe gestures are added to the result's label, so we can swipe in order to clean the result, or even undo or redo our actions. Brackets that can be used with ease, and Numerical will evaluate your calculations in BEDMAS order.