A fun display to count the days until a baby's due date
For one of my kids, we announced my wife's pregnancy by creating a tiny little count up clock.
The board was an Arduino Nano connected to a real-time clock module and a SSD1306-based OLED display (the first line of text was yellow, and the remainder of the display was white). The whole thing was wired as closely as possible and jammed into a tiny project box which was almost exactly the right size to hold it all.
We gave the tiny little clock to my parents for Christmas, it took a while for them to figure out what it was... and what it meant... but that was all part of the fun.