Glowtape is a unique DIY wristwatch by Henner Zeller that uses glow-in-the-dark tape and an RP2040 microcontroller to display the time.
Watchy is an open source E-Ink Smartwatch with an MIT license. Development resources and documentation can be found on the official website watchy.sqfmi.com. There are also several retailers selling the watch hardware. See the documentation for instructions on how to get started with developing for Watchy.