Qemu is one of the early virtual machine systems. Before Xen, before VirtualBox, maybe even before VMware, Qemu was the cross-platform, FLOSS option for running virtual machines and even running cross-architecture VMs. I think some of its code has been incorporated into these other big-name products.
If you have an ISO file that you need to boot for testing purposes, it doesn't get much easier than using Qemu. For being a FLOSS app, the command-line interface is a bit Windows-centric in it's drive naming (the C drive is the first hard drive file that you attach; the D drive is cd-rom iso file), but it gets the job done:
$ qemu -cdrom ./debian-7.0.0-i386-netinst.iso -boot d
According to the webpage, "when used as a virtualizer, QEMU achieves near native performances by executing the guest code directly on the host CPU." That's impressive. Qemu is still in development.
If you have an ISO file that you need to boot for testing purposes, it doesn't get much easier than using Qemu. For being a FLOSS app, the command-line interface is a bit Windows-centric in it's drive naming (the C drive is the first hard drive file that you attach; the D drive is cd-rom iso file), but it gets the job done:
$ qemu -cdrom ./debian-7.0.0-i386-netinst.iso -boot d
According to the webpage, "when used as a virtualizer, QEMU achieves near native performances by executing the guest code directly on the host CPU." That's impressive. Qemu is still in development.