ChromeOS Flex
ChromeOS Flex, developed by Google, is a free and lightweight Linux distribution based on Gentoo-derived ChromeOS. Unlike ChromeOS which is designed specifically for Chromebook computers, ChromeOS Flex can be installed on most x86_64 devices with a AMD or Intel processors, offering a Chromebook-like experience.
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MiniOS
MiniOS is a Debian-based Linux distribution which strives to be lightweight, modular, versatile and customisable. It comes in three editions, "Standard", "Toolbox" and "Ultra".