It's Chrome OS. It runs a Linux kernel but by default it's designed to be a very simplified, locked-down OS that runs the Chrome browser and Android apps. It a

It's Chrome OS. It runs a Linux kernel but by default it's designed to be a very simplified, locked-down OS that runs the Chrome browser and Android apps. It also has a built-in Linux development environment that you can enable, which runs in a mini VM. It gives you a full Debian system, without any risk of messing up the built-in OS. If you don't want Chrome OS at all, it's definitely possible to just install Linux.