This is a two-part charging dock for the Apple Watch.
Part 1 (stand) holds the wireless charging puck in place. Part 2 (shell) slides on top, and provides a place to set your Apple Watch. Slots in the sides of the shell hold the watch steady by its band, while the magnetic charger keeps it in place to charge. The screen lines up with the Mac's screen, so you can see the display while the watch is in Night Stand mode.
Don't have a 3D printer (yet)? Printed models are available at Shapeways:
Available in Mac Plus: https://www.shapeways.com/product/G7DAQ2MJF/apple-watch-dock-mac-plus
Note: Requires the insert to hold your charger:
Painted and finished models are available at my Etsy store: https://www.etsy.com/listing/255372973/classic-macintosh-styled-apple-watch