What software is missing from Linux? I've written a text editor and a window manager in the past.
"CAM" is computer aided machineing and it is software that takes a 3D model and a lot of machine parameters in, including size of the cutting bit and etc, and produces "g code" which is movement instructions for a computer controlled mill of some type.
It is the equivalent of the "slicer" in 3D printing.
But for milling or subtractive manufacturing there are many more details, and there needs to be a way to visualize and simulate the toolpath, and edit it by hand.