About 18 months ago, Google acquired Neverware, a company who took the open source version of Chrome OS and customised it for the schools market.

The new version of Chrome OS, called ‘Flex’, can be installed on pretty much any device and also includes Linux containers. Interesting!

Google is positioning Chrome OS Flex as an answer to old Mac and Windows PCs that might not be able to handle the latest version of their native OS and/or that might not be owned by folks with budgets to replace the devices. Rather than buying new hardware, consumers or IT departments could install the latest version of Chrome OS Flex.
Source: Google turns old Macs, PCs into Chromebooks with Chrome OS Flex | Ars Technica