The 1.6.1 version of IntCalc for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The actual developer of this free Mac application is Inertron Software. The application is included in Productivity Tools. We recommend checking the downloaded files with any free antivirus.
From the developer:
IntCalc is a RPN calculator, loosely based on the ancient HP16 programmer's calculator. It can display and switch between any of the common number bases, and therefore can serve as a hex calculator, a hexadecimal conversion calculator, a hex to decimal calculator, an octal to hexadecimal converter, etc. Each element can be individually displayed in any number base - binary, octal, decimal, hexadecimal, or ASCII.
You may want to check out more Mac applications, such as RubyCalc, InstaRate or GraphingCalculator, which might be similar to IntCalc.