elementary OS
elementary OS is an Ubuntu-based desktop distribution. Some of its more interesting features include a custom desktop environment called Pantheon and many custom apps including Photos, Music, Videos, Calendar, Terminal, Files, and more.
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SmartOS
SmartOS is an open-source UNIX-like operating system based on illumos, a community fork of OpenSolaris. It features four technologies - ZFS (a combined file system and logical volume manager), DTrace (a dynamic tracing framework for troubleshooting kernel and application problems), Zones (a lightweight virtualisation solution), KVM and bhyve (two full virtualisation solutions for running a variety of guest operating systems, including Linux, Windows, BSD and Plan9).