Fuchsia is the name of an in-house OS Google has reportedly had in the works for years. Now, it is finally due to see a roll-out on one of the OEM's more recent smart-home products. The Nest Hub is slated to start using this new system in an impending update.
https://www.notebookcheck.net/Google-will-finally-launch-Fuchsia-OS-soon-albeit-on-just-one-smart-home-device.541038.0.html