Over four decades ago, when I was in my pre-teens, my family had a TRS-80 Model 1 (or was it a 3?), and I created a simple game for it in BASIC. In the game, a maze-like wall of blocks would be built as you watched, each block one of the system's super-chunky monochrome pixels. When the wall became almost, but not quite, impassable, you'd hit the space bar to halt the construction and begin the next phase of the game…
Thanks for sharing, and it is a touching present for a dad :)