Qubes OS
Qubes OS is a free and open-source, security-oriented operating system for single-user desktop computing. Qubes OS leverages Xen-based virtualization to allow for the creation and management of isolated compartments called qubes.
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Vanilla OS
Vanilla OS, a fixed-release distribution based on Debian (formerly Ubuntu, prior to version 2) with the GNOME desktop, is an immutable operating system. The core parts of the system are locked down to prevent unwanted changes and corruption from third-party applications or a faulty update.