For the past few months I have been working on and off on a ULP script that would allow for double sided PCBs on my home CNC machine. The script is 95% finished and I have been using it for a while. I recently ran into an issue where my older 5.x license of Eagle PCB was causing problems with the latest 7.x version of Eagle. Because of this I am trying to Kickstart an upgrade of my Eagle license in return for access to my ULP script that allows for double sided PCBs on a CNC, as well as allowing for non-square shapes.
Take a look at the campaign here: Eagle PCB update for CNC Double Sided PCBs