For a long time, I was using Linux-VServer (that's a "BSD jails" equivalent for Linux). It worked really well. But it allowed only for Linux guest systems, and

For a long time, I was using Linux-VServer (that's a "BSD jails" equivalent for Linux). It worked really well. But it allowed only for Linux guest systems, and the virtual networking often had some unexpected holes and flaws (maybe "BSD jails" work better in that regard). However, with the arise of KVM (and other virtualization systems that no longer slow down your guest systems), I'm switching to KVM for those tasks.