Casio's F-91 wristwatch is available in many colors and materials and is famous for its overwhelming success and its designation as a "terrorist" signifier by hysterical U.S. investigators who found them being used as a timer in bombs. Casio has neglected to make a smartwatch version—it is very compact, after all—but an aficionado has stepped into the void. Behold the F91 Kepler, a custom-made smartwatch that uses the classic chassis.
The F91 Kepler is complete redesign of the classic Casio F91W watch. This project completely replaces the original internals of the watch only keeping the original case and adding an OLED display and a bluetooth capable MCU. This repo contains all the firmware, hardware, and completely unfinished software (phone app) ;).