GeekCalc is designed for the software developer. It includes the basic calculator functionality but also supports signed and unsigned integer math for 64, 32, 16, and 8 bit integers. An ASCII mode and an ASCII character table are included as well.
The calculator was developed as an exercise to learn Objective-C and the OS X development environment. The calculator seemed like a simple way to start and it also gave me a calculator that has the features I haven't been able to find in any other free calculators.