Hardware - just stuff I had laying around, really...

• - Lego Egg-lathe, directly driven by a stepper
• - Lego linear motion stage, built from tracks of that Lego Boost robot
• - ESP8266
• - 2x A4988 drivers.
• - a proximity sensor for end-stop detection

Firmware - Arduino-based, aREST-based stepper motor driver, exposing a few operations:

• - Rotate egg by X degrees
• - Move pen to 0-100% position
• - Move pen by X%
• - initialize
• - pen up/down

Software

Blockly-based UI, in fact a modified MusicMaker example

• - a few custom blocks translated to the exposed REST methods

Yeah, yeah, I hear you: 

• - The X stage is stupid, the pen should be moving parallel to the egg surface, otherwise it doesn't paint straight.
• - Egg coupling is shaky and doesn't "grab" well enough. Sure, it's built with Lego wheels!
• - Pen is shaky! It's mounted too far from the egg.
• - etc etc.

Well, sure! But if we'd want here the EggBot, we'd buy a EggBot! We're just having fun here :)