Post One Nest is a private home automation project. It runs on a single computer inside one family home and connects that home's own Google Nest thermostats and cameras to the household's own automation, so that heating, cooling and lighting can follow the household's routine.
It is used by one household only. It is not a product, it is not offered to the public, and nobody outside the household can sign in to it or use it.
How the project handles data is described in the privacy policy.