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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Tiny Core Linux
Tiny Core Linux is a 16 MB graphical Linux desktop. It is based on a recent Linux kernel, BusyBox, Tiny X, Fltk, and Flwm.