[akashv44] has gone a simpler route, designing their own from scratch with a bare PCB design ... It’s a simple smartwatch, but nonetheless one that teaches all kinds of useful skills in embedded ...

Enter the Open-SmartWatch from [pauls_3d_things ... but there’s also an enhanced edition of the PCB that adds another 4 MB of RAM, a micro SD slot, and a Quectel L96 GPS receiver.