From Nikola Stepan:
CalcSharp is .Net calculator that evaluates mathematical expressions step by step. Features: Evaluate mathematical expressions step by step. Large number of built-in functions and operators. Large number of predefined mathematical, physical constants. Supports fractions, decimal, hexadecimal, octal and binary numbers. Ability to express angles in degrees, radians, or grad. Works with Infinity and not-a-number. User-defined variables. User-defined functions. Three kinds of parentheses detail error checking and reporting. Unlimited size of expressions. Unlimited depth of nesting Expression builder. Stores expressions in plain or rich text format MDI support. Log successfully calculated expressions and results. Tray and hotkey support Multilanguage support.