Another one, I built one of the originals a while back and have been procrastinating on actually getting the PCBs I designed for the GPS version manufactured:

https://open-smartwatch.github.io/

Recently purchased a PineTime and have been very impressed. It's more comfortable than my Casio F-91W.

The battery life also seems significantly better than advertised. I unboxed and charged to 100% on 13th November, and now on 21st November it's sitting at 43%. I wake the display up maybe a dozen times per day to check the time, read notifications, or pick up a phone call.

Updating the firmware was a breeze, the thing just works. Only snag I've noticed is that the pedometer is too sensitive, with no obvious way to adjust sensitivity.

I haven't risked showering with it yet, but it's supposed to be waterproof up to 1 meter. I suppose this implies it wouldn't survive a swimming session though.

I own one, mine's really waterproof, I almost always forget to take it of when doing the dishes or bathing the baby. Agree, it's great, I only wish it had some kind of transflective lcd screen ( like the garmin's ) : better battery life and always readable screen...