Commercial eye tracking has been around quite a while, and it is quite expensive, specially the ost-processing software tat extracts "useful" data from the tracked movements. But the open source projects are quite new, appearing mostly the last decade, with a huge increase last few years. One of the earliest and best documented is the EyeWriter . I wont start enumerating all the references I've analyzed, but if you are curious just search for "open source eye tracker". Here is also a nice eye-tracker link collection, for your reference.
One common thing among these projects is that, for their purposes, they need accuracy and speed (which is not our case) so they rely on hardware that is either not portable or too big or expensive for the goals of the Crazy Eyes project.
So far the projects that match more closely what we want are open source general purpose programmable computer vision modules like Ibrahim Abdelkader's OpenMV , or small linux systems like the one used in the Eye of Horus project (just to mention some references). But they are still to costly for the cheap hilarious gadget we want to play with in Halloween or some cosplay game, or even in a party!
Another remarkable computer vision experiment that really inspired me is John Orlando's AVRcam, where he interfaced a sensor with just an ATmega8 back in year 2004, 12 years ago!.
Two years ago I got involved in a project for a big company that wanted to promote their new robot film saga with an actor performing as one of the robot characters in mall centers an other places. I was in charge for the special effects of the dress, like voice changer, moving lights while speaking, mechanical sounds for the legs and arms movements, a pari of animatronic eyes controlled by the actor with a joystic, etc.
When I fist searched about animatornic eyes, both commercial and open source, i was surprised that there were not so many options, most of them expensive and bulky, even if it was all two servos and a few simple mechanical parts. So i decided to take advantage of my brand new 3D printer and made the animatronic eyes shown in the previous log. They are available in my thingiverse.
These were ok to fit inside the robot's helmet, but for the Crazy Eyes I want something even smaller and easier to assembly, so I'll be working on a new design at the same time as testing the tracking capabilities of several microcontrollers.