ChromeOS Flex is an interesting one; it’s definitely not as flexible as a proper Linux distro but if you need something simple and hard-to-break to run on an old machine (for instance for an elderly relative who’s still using Windows XP) then it could be worth a shot. That said, I’m now investigating whether Linux Mint is a better choice for my own elderly relatives!
I think it used to be called “cloudready” until Google bought it and made it official. It seems like it’s aimed more at businesses and schools that want a fleet of Chromebooks, but it seems alright for the casual tinkerer too.