With all that I've written recently about 3D printed clocks, I thought I should not neglect a purely electronic one. Some while back I bought a M5Stack. It's a packaged ESP32 with a screen and (in this model) some neopixel LEDs. I wrote code to use this as a clock. It periodically resyncs to a reference time if it has a wifi connection and otherwise tracks the time internally. This variant of the M5Stack doesn't have a real time clock, but there is a library for tracking the time without one. The colored LEDs on the side very gradually change color: a color encoded as HSV is picked at random and the color change until it reaches the target value. It can run off the internal battery or from USB power. Here's a few minutes of it, at 30x speed:
Not super interesting, but practical and useful.