It's FOSS - https://itsfoss.com/goobuntu-glinux-google/
Brief: For years Google used Goobuntu, an in-house, Ubuntu-based operating system. Goobuntu is now being replaced by gLinux, which is based on Debian Testing.
If you have read Ubuntu facts, you probably already know that Google uses a Linux distribution called Goobuntu as the development platform. It is a custom Linux distribution based on…(easy to guess)… Ubuntu.
Goobuntu is basically a “light skin over standard Ubuntu“. It is based on the LTS releases of Ubuntu. If you think that Google contributes to the testing or development of Ubuntu, you are wrong. Google is simply a paying customer for Canonical’s Ubuntu Advantage