Is there any realistic free alternative for 3D (not 2.5D) parts?
You certainly won't want to use it for mass production, but for hobbyist use where getting the model and CAM config right, setting up the machine etc. are the biggest time sink and most parts are made in quantity 1, I found it acceptable.
FreeCAD has a built-in CAM. It's not very powerful, but it's only going to get better with time (while the proprietary alternatives will only continue to get worse as companies try to squeeze money out of their users).
The free CAM available in F360 has been artificially limited to only allow extremely slow travel speed. It's almost useless.