This is an Arduino-based 3D-printed watch. By not including fancy Wifi and BLE connectivity, it gets several months of run time out of a 160 mAh button cell. The display is an always-on 96 x 96 pixel Sharp Memory LCD. If telling the time is not enough, you can play a simplified version of Flappy Bird on it.
More Information on Hackaday.io: https://hackaday.io/project/12876-chronio
BQ Prusa i3 Hephestos
The parts I made were printed in PLA.
Buttons and cover should be printed with thin layers (<100um).
The case needs to be printed with supports. Simplify3D is not required, but will save you some time needed for removing the supports.