Xen
Today someone told me about
Xen. I had heard of it (and even used it) a little some time ago, but didn't look in details at it. But now it seems very interesting. For now, on my server, I'm running
Linux VServer, a patched linux kernel that allow you to run different linux distributions at the same time, on a single computer. The patch actually only add a few things like "security contexts", then we run each linux distribution in a chroot, in a different security context. This mean that each instance is almost as fast as if it was running directly on the machine (and actually it is). The problem is that each instance is using the same linux kernel, so this is probably not as secure as a system running a different kernel for each instance. And it can also be a problem if you want customs kernels for each instance.
Xen seems to be very fast too, doing this in an interesting way (and I see they plan to use the hardware support AMD and Intel recently announced). So I'll have to try Xen, and see if I can use it to replace linux vserver on my server. This would also maybe allow me to have an OpenBSD or FreeBSD running on the same computer.
What I like with virtualization is that it's easy to keep a backup of a running system and restore it easily on a different computer.