That is using messaging for the web through Google Fi. But there is little reason to do that now as Google messages the app itself can be used through messages.google.com. there are several stand alone computer applications that use the portal as well (messages in the windows store, messages or google-messages package in most distros. Dunno about Mac. Either way, instead of fi being the backend, the app connects directly to your PC. You just have to pair your phone using the app directly.