QEMU
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QEMU is a portable virtual machine emulator. It lets you run other operating systems in windows on your desktop.
[edit] Typical usage
qemu-system-x86_64 -usbdevice tablet -enable-kvm -net nic -net user -m 768 -vga std /dev/sdb
[edit] ISO images
qemu-system-x86_64 -cdrom linuxmint-11-gnome-dvd-64bit.iso -hda /dev/sdb -boot d