This is a charging dock for your Apple Watch.
Part 1 (stand) holds the wireless charging puck in place. Part 2 (shell) slides on top, and gives a place to place your Apple Watch. Slots in the shell's surfaces hold the watch stable by its band, while the charger keeps it in place to charge. The screen lines up with the Mac's screen, while the watch is in Night Stand mode so that you can see the display.
Printed, finished and painted versions of the dock can be found on my shop: