From Forum Nokia Wiki

Calcium is a fast, easy to use calculator for your S60 phone

Getting tired of the S60 calculator? We were, so we made our own. Using some of the concepts that make ControlFreak so easy to use, we removed the need to select on-screen buttons and moved all the operations to the joystick. Doing basic calculations on your phone is now only a couple of clicks away.

http://mtvoid.com/calcium/index.html