Harmony
There are no good simple MP3 players you can buy anymore. The iPod is discontinued, the modern alternatives are either iOS apps or weird overpriced audiophile bricks, and nothing is just a small thing with a wheel and a screen that plays the music on the SD card.
So I’m building one. ESP32 microcontroller, MicroPython, a screen, a rotary encoder, an SD card slot, headphone out. The Python core is hardware-agnostic and runs in a PC simulator for testing — the physical device is just one of the targets. Mark 2 is the current attempt; Mark 1 taught me what I needed to know to start over.
It is the most fun I have had with a computer in years.