Soli Sandbox is a way to connect your web prototypes to Soli interactions on Pixel 4.[1] Create a prototype on your computer, and set it in motion with Soli gestures through the Soli Sandbox app. You’ll be able to use touchless swipes, taps, and more in your own prototypes!

[1] Soli functionality only available on Pixel 4 in the US, Canada, Singapore, Australia, Taiwan, Japan and most European countries.

Note: Soli Sandbox is not a tool for creating production apps.
From version Soli Sandbox 1.1.0(29):
Soli Sandbox is now available in the following countries: Australia, Ireland, Japan, United Kingdom, and Singapore.
All versions
September 2, 2020