UPD 20181008: There is an updated version of this board here: https://www.thingiverse.com/thing:3142989
This is a compact steno keyboard for Plover.
Numbar is replaced with a single key between the vowels.
Matias switches are inserted from the inside - to reduce the space between the flat key-tops and the board surface.
The bottom plate supports switches, so the wires should go around the key switch case centers.
Electronics taken from QMK/Planck project, layout modified for the 5x5 matrix.
The tray is supposed to hold the keyboard, an HP Stream 7 Windows-based tablet, a modified USB hub and a battery that supplies the power to keyboard.
IMPORTANT: The keyboard case and the bottom case plate need to be mirrored either in X or Y direction, so there are more keys on the right side. See the pictures for the reference.