The original egg-bot features two steppers for rotating the egg and moving the pen, lifting the pen is done by a small servo.
The controller for the motors is the EBB (EiBotBoard or EggBotBoard i think), it is a controller/driver for two steppers and a servo which is based on the UBW (USB bit whacker) board which is basically a usb device for controlling multiple servo/stepper motors (http://www.schmalzhaus.com/EBB/
). Together with a driver, and the correct firmware one can send a set of defined commands to it to move the motors. Eggbot programs are basically a series of commands to rotate the egg/pen and to lift the pen. There exists a inkscape Plugin to generate UBW-Commands for the eggbot.
And that's the part I didn't like so much about the eggbot: it is using a pretty custom set of software/hardware tools to operate, although there are already plenty of other great tools for these CNCish kind of tasks.
Recently I have built a desktop cnc milling machine (http://www.instructables.com/id/Easy-to-Build-Desk-Top-3-Axis-CNC-Milling-Machine/) with the appropriate driver (http://www.instructables.com/id/Easy-to-build-CNC-Mill-Stepper-Motor-and-Driver-ci/).
So I decided to alter the eggbot design a little bit, so that it is driven with three stepper motors (without a servo). Therefore it can be controlled with any cnc software (and I could reuse my old controller/motors)