Smart mirror is an open-source web app which lives on a iPad behind a two-way mirror in my living room. The app supports a number of modules, including date & time, weather, subway status, chores, and music currently playing.
The concept behind a mirror display is simple: a two-way mirror allows half of any light to pass through in either direction. This means that if there is an imbalance in brightness on either side, it will appear transparent from the darker side. The mirror is backed with black construction paper, and the display is white text on a black background, which makes everything appear reflective except for the text.
I also designed and 3D printed a frame to hold the iPad to the mirror. It has a removable side, facilitating the easy removal of the iPad, as well as slots for its cable. The 3D models were coded in OpenSCAD.