The "Ass-Backward Calculator" for the Apple //GS - an RPN calculator NDA
The source code is built using my Apple //GS Build Pipeline. If you setup all of the prerequisites on that project, you should be able to build this on a Mac using Xcode. Failing that, put the source onto a real or emulated GS and build it using ORCA/C. However, I no longer have a GS compatible Makefile. If you look in the git history, you will see that in the past, the build could be done using dmake under GNO/ME on a GS.
The abCalc binary is a shell command you can use from GNO/ME:
And abCalcNDA is a new desk accessory which you can use from within GS/OS applications: