My quest for programmable smartwatches lead me to a lot of googling sessions, during which I've discovered BangleJS, open source smartwatches programmable with JavaScript.
Every time I find Greenspun's tenth rule in the wild, I add a link to the project and update a counter.
I've bought Pebble time steel smartwatches with the idea, that I'll try to program them. This didn't go well for several reasons.