What is Reddit's opinion of HeeksCAD?
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➔ HeeksCAD website

This list is about 3 years out of date, but check:

Also, I understand they're working on adding CAM features to Freecad, so check there.

Also, there's a CAM add-on for blender under development, see here: http://blendercam.blogspot.com/ . I've never used it.

Checking synaptic on my 14.04 Ubuntu machine, "gcode" finds:

pcb2gcode repsnapper (for 3d printers) sfact (same)

You may or may not like openscad; I suggest you take a look at it. I've fooled around with it a little.

Finally, you might want to check out Heekscad:

And the programs that come with linuxcnc these days.