I believe it’s C++ and seems to use the QT toolkit.
I doubt it will be opensourced, folks have asked, and it’s viewed as a competitive advantage.
There are a number of other opensource CAM tools which could use help though, see the list at: https://wiki.shapeoko.com/index.php/CAM
In particular, MakerCAM looks like low-hanging fruit and really needs to be ported to node.js or something similar.
FWIW, I’ve been working on a hybrid system which uses OpenSCAD as a front-end and then some other tool (LuaLaTeX and METAPOST for one iteration, currently experimenting with TPL (see https://tplang.org/ ) and am considering some other options — hope to submit it to Kickstarter at the beginning of next week.