The author, an embedded systems engineer, created a cheap, Linux-capable business card form factor device using the F1C100s processor. The device costs under $3 and is a complete, minimal ARM computer running customized Linux firmware built with Buildroot. It has a USB port in the corner and boots in about 6 seconds, showing up as a flash drive and a virtual serial port that you can use to log into the card’s shell when plugged into a computer. The author designed and built everything himself, and the entire device is RoHS-compliant. It lacks I/O, networking, and storage for heavyweight programs but includes console games like rogue, 2048, fortune, and a MicroPython interpreter.
https://www.thirtythreeforty.net/posts/2019/12/my-business-card-runs-linux/