Hi Clive, nice to be here, thank you :)
Here's a CNC shield:
http://ooznest.co.uk/Premium-Arduino-CNC-Shield
I'm designing and building a basic budget machine from some scraps I have and this system is open source and let's me run a basic CNC on a £15 system!
I've seen linuxCNC and it does seem good! I think I will try it if Fusion 360's CAM environment lets me down.
Why I say it's less advanced?
Firmware - on a 3D printer you modify the firmware as code and upload it as a very powerful and intuitive system with inbuilt support for autolevelling, LCD screens, SD cards and much much more. The most decent CNC firmware I can use is GRBL which uploads in a weird way and has very few settings.
Hardware - now here I am talking about open source and affordable, not the awesome professional machines you use!! With a 3D printer almost every single motherboard can very easily attach to a screen, SD and can be set up for many different forms of machine. With the CNC it only has axis, spindle controls and endstops. If I want to run it headless I have to attach a separate Arduino to relay instructions!
On top of that, on my printer I use "Octoprint" which allows me to control it over the web from anywhere in the world securely. The best for CNC seems to be "GRBLweb" which is also less developed. I may be able to edit octoprint for the CNC though.
Software - there are many clean and easy to use printer softwares that have a very nice and intuitive gui as well as much deeper controls. As a professional 3D technician I use Simplify-3D, one of the few paid slicers. I'm struggling to find anything on-par for CNC but Fusion 360's CAM may help!
Also the documentation is horrendous!
Please note I'm just talking about the entry level open source machines and not the professional ones, which I only dream of owning. For various reasons I'm having to go opensource.
Thanks!