Nice and Easy to use.
This is an outstanding calculator for your PC. I wish I had this one for real (or my cell phone). The programming capabiltities are very nice and easy to use. It would be even greater, if you would split this project into two parts (GUI and calculator.dll) so one could change the skin or embed it into self-made applications more easily.
Many calculators and spreadsheets out there are limited by double precision (e.g., 15-16 significant digits). Sometimes you need a program that is not. This is that program! You can enter a full expression in the top left pane and see the result in the bottom left pane. All the normal functions of a scientific calculator are there, including base conversion, deg/rad/grad conversion, output as fraction or decimal. You even have a macro language for writing mathematical functions with multiple inputs and outputs.
Very useful, especially the built-in functions.