Let me tell you that we do not have the plans, yet. The author writing on Medium has teased up about sharing the details of this DIY project.
We know from one of the images that it runs of an Amazon Fire Stick with a custom APK (Google app if you prefer). He stuck a transparent screen between the two-way mirror and the cabinet door. The rest is off-the-shelf parts that could not add up to more than 100$.
I really look forward the details, especially the “couple lines of code” app he built. There are so many possibilities with this kind of software! If you have a mirror in a common space of your house, it could display each family member schedule, the weather and a shared to-do list. Perfect family organization!