Is there an equivalent to Grbl for Excellon PCB drilling? For CNC milling we have code such as Grbl Controller in the PC, and Grbl itself in an Arduino, and these handle the appropriate G-code files. Is there an equivalent package to handle Excellon files and drive a 3-axis drilling machine?
No, there is no existing Arduino library to parse Excellon format drill files in order to control a drilling machine. Looking at the specification it looks to be very similar to G Code, and some brief googling shows that there are various utilities for converting it to G Code that could be run from something like grbl.