Qubes is an operating system based on the principle of security by compartmentalization.  Using the bare-metal hypervisor Xen, it reduces the trusted code base, isolates network cards, USB controllers, the GUI, and other domains with predefined purposes and levels of trust.  However, it is currently only operable on the x86 instruction set.  Power ISA is the only open source ISA that has actual open source implementations (SBC's) on the market.  This makes it significantly more secure.