Of Itself So - A Summary of Gerber to GCode Isolation Routing Software
"... and no one shall work for money, and no one shall work for fame; But each for the joy of the working, and each, in his separate star, shall draw the thing as he sees it, for the god of things as they are"
According to the wiki: pcb2gcode is a command-line program that calculates machine toolpaths from given PCB layouts. It is free and open-source and runs on Linux. Requires things like libgerbv to be installed.
From the web page: This is an open-source freeware which open Gerber, Excellon or G-code, edit it or create from scatch, and output G-Code Isolation routing files. Offers both a Windows and Linux download.
From the web page: The Line Grinder is a software package which can generate isolation routing GCode from the Gerber format plot files output by most PCB design programs. It runs on Windows, is free and open source.