Key Features:

• Supports a rich expression format, which is in most cases identical to what you would type in your programming language.
• Support for adding unlimited numbers of variables.
• Built-in debugger that lets you see the expression simplified step by step.
• Debugger Back-step lets you backup as many steps as you like so that you can replay critical operations.
• C/C++ operator precedence
• Mouse optional, all calculator commands and functions can be done using the keyboard alone.
• Mini-Calc Mode lets your calculator take up very little screen real estate, and yet remain entirely usable.
  
• Numerous built-in unit conversions (memory sizes, lengths, areas, volumes, temperatures etc.)
• Built-in great circle route and straight line distance calculators.

Input/Output Formats:

• Binary, Octal, Decimal, Hexadecimal, Booleans, Characters, UTF-8 (out only), and UTF-16 (out only)
• Convert automatically between these types in your expression with the keyboard, a button, or a contextual menu.

Operators and Functions:

• Standard: Addition, Subtraction, Multiplication, Division, Modulus, Power, Square Root
• Grouping: Parenthesis
• Variables: Previous Answer
• Bitwise: complement, and, or, xor, shift left, shift right
• Comparators: equals, less than, greater than, less than or equal, greater than or equal
• Logical: and, or, and not
• Trigonometric: Sine, Cosine, Tangent, Arc-Sine, Arc-Cosine, Arc-Tangent, Degrees To Radians, Radians to Degrees
• Other: Min, Max, Round, Ceiling, Floor, Absolute Value, Sign

What users are saying:

• Very very useful little app, well worth the money the author is asking for! -- ScottM review of Mac OS X version on MacUpdate.com
• This is a very nice and unique calc, and they are steadily improving it. I'm giving it a five for current usability, improvements, and a GREAT price. Get it now, before demand drives up the cost. -- MikeyK review of Mac OS 8/9 version on VersionTracker.com