There's also the point that SokidWorks costs $4000 minimum! (Excluding the student license).

For many purposes, such as the author sharing his designs with random viewers, that makes it a non-starter.

An alternative commercial program (not OSS), but free for Hobbyists is Autodesk Fusion 360.

It does have significant drawbacks... but if you're just getting into CNC stuff, it has fairly decent CAM functionality in built, making it a reasonable intro thing. :)

Absolutely second this. Fusion 360 is far from perfect but it does provide some approximation to real parametric modeling. OpenSCAD lacks very basic features by comparison (e.g. you can't even make real cylinders). I forget the exact licensing terms (I'm using an edu email address), but they basically seem happy for it to be used for free for non-commercial purposes. I think the pricing is quite reasonable in any case.

Hmm, it looks like that's only free for 30 days?

It shouldn't be. It's supposed to be for 1 year, and be renewable. I've been using it on and off for a few months now, without issue, if that helps. :)

You're right, they mention somewhere you open up the trial and select "I'm a hobbyist" and it becomes free, thanks!

Yeah, I guess I should have added this to the question. I just started making hardware designs, so I want to make simple things like boxes to put my hardware in, or other sorts of enclosures. Nothing as complicated as a motorbike, just boxes with at most a few parts.

Plenty of good (considering their costs) 3d-printers designed in OpenSCAD, which are a kind of CNC machine.