This isn't really a game - unless you consider it a short "Walking simulator" - it's more of a tech demo.
The engine is a basic Wolfenstein-3D like 3D engine. It has floor and ceiling textures and render reasonably sized and complex rooms at 60 frames-per-second, in a 128x96 viewport.
If anyone feels like something out of it, it's fairly easy to get started with (details below).
The bottom left sprites are walls, except the left-most one which positions a door.
The next row up is for placing objects.
The numbered circles are for placing triggers that trigger code when the player reaches them.
The gray arrows at the top are for setting the player start position and direction.
You can use the top left 124x32 tiles of the map area.
Wall textures (and door texture) are sprite tabs 2 and 3.
You can define up to 8 (including the door).
Objects are sprite tab 4.
They are always 16x16 pixels. You can define up to 16.
Objects must be defined in the "otyp" array (code tab 1):
Floor and ceiling textures are defined at the very right of the map.
Floor and ceiling "plane types" must also be defined in code tab 1:
You then select the floor and ceiling planes by setting the "floor" and "roof" variables.