This is a nice post about how to create an open source CNC:
This CNC uses an Arduino board with a CNC Shield. This CNC Shield could be replaced with this one:
The software used to control the CNC is called GRBL and it was developed in C and could be flashed on Arduino board:
Unfortunately this software is not (yet) portable, this means it is optimized to run on AVR microcontroller only. Then it will not work directly on Raspi.
Other missing part is a graphical interface to use whit GRBL. I missed the GRBL Controller used to control and monitor it.
Update: Although you cannot run GRBL direclty on Raspi, you control the Arduino CNC from it: