This is A smart watch based on STM32 & LVGL & FreeRTOS, the total cost is about 100 RMB which equal to about $20 USD. All the hardware & software & 3D print shell are finished by my self, you can freely modify them if you want. The functions of this watch includes basic watch's function, calculator, timer, calendar, NFC card storage, games, use Bluetooth connect to smartphone to synchronize time & data, etc. It also can add some other apps. Till now, the version is v2.3.2, and the ROM cost is only about 350kb. Want see more please go to my github.
Very mouthful name for smartwatch
Aside from that actually is nice to have open source smartwatch
https://pine64.com/product/pinetime-smartwatch-sealed/
I have a couple of these watches. They’re basic, but capable.