Hi Tristan,
There's no secret about the source code - it's open source, but I haven't formalised the licensing yet. It can almost certainly be built on a Mac, because the development system I use (Lazarus/Freepascal) is a multi-platform system which includes MacOS in its supported list. You can't just take the source code and rebuild it on another platform - you need to install Lazarus and do some necessary configuration, then load rs-ux, modify it as necessary for the platform, then build it from there. If you're familiar with Lazarus it's straightforward, otherwise it would be a bit of a challenge.
The current state of development is that I completed a version 0.6, but didn't release it because I decided to do some major rewriting of the graphing sections of the program. So it's in a state of flux, but v0.6 is usable. If you can make use of its source code, let me know and I'll package it up and make it available.