Google Assistant launched with support for a handful of apps and services, but the number has rapidly expanded since then. Today, there are a few new markers of smart home devices that are part of the Assistant family. You can now use Assistant to control devices from iHome, Leviton, Emberlight, and Artik Cloud.
You likely don't know what all these companies do—there are roughly a billion smart home startups now. Emberlight sounds like a maker of smart light bulbs, but it actually makes smart light bulb sockets to turn existing lights into smart ones. iHome makes a lot of things, but in this case it's the smart plugs that have Assistant support. Leviton meanwhile makes a number of smart switches and outlets. Then there's Artik Cloud, which is a Samsung-owned online IoT platform that connects many devices like Hue, WeMo, Kevo, and many more. In this case, it's only Legrand smart hubs that are supported.
You can play around with all these now by linking your account in the Home app.