Pokétch-os is a fork of wasp-os, an open source firmware for nRF52-based smart watches. It reskins watch applications to emulate those found in the Pokétch, a digital watch given to players in the 4th generation Pokémon games.
To install, you can follow the wasp-os installation guide. I've only tested this for the P8 watch.
Currently, I've only themed the digital watch and stopwatch applications. Now that I've gotten over the initial hurdles (compiling apps, displaying images, uploading to the hardware, etc.), in the future I'd like to expand on this project and create my own apps in the spirit of those found in the game.