G-code firmware for handheld plotter (Arduino)
Your question may be useful to people interested in 3d printing (the purpose of this SE Site) so, even though you're not asking a 3d printing question per se, I think this answer will be helpful...

GRBL:

GRBL is a well known and mature g-code interpreter that will run on an Arduino Uno and is free and open source.  Check it out here.

I hope this helps!  :-)