PebbleOS isn't the only player in this space. There's also https://www.espruino.com/ which powers https://banglejs.com/. It's a tiny implementation of Javascript for microcontrollers, so it's really easy to hack your device in real time.

It also powers the Fallout Pip boy and possibly some other stuff from the wand company: https://www.thewandcompany.com/fallout-pip-boy/ See: https://github.com/orgs/espruino/discussions/7577