Some more virtualization projects worth investigating:

• Linux-VServer
  Linux guests on a host Linux system, using operating-system level virtualization. It uses what it calls "security contexts" to create virtual private servers in userspace. These security contexts are built with ordinary Linux tools like chroot, quotas, and routing. The kernel is unaffected- the virtual private servers share hardware efficiently, so there is very little performance hit. Users see only their own little virtual spaces. GPL and free of cost.
• QEMU and Bochs are emulators that replicate hardware functions in software, even hardware that is not physically present. So you can run unmodified guest operating systems in all manner of virtual hardware configurations. QEMU is GPL except for the QEMU Accelerator Module, which is a proprietary product. Bochs is LGPL.
• Ensim is a closed-source commercial family of products designed for Web hosting and delivering Web applications. Ensim uses a "private server technology" that sounds a lot like the concept behind Linux-VServer and Virtuozzo, operating-system level virtualization.

Resources

• Feeling New Heat, Red Hat Rolls On
  
• QEMU: Maybe a VMWare Killer, Maybe Not

This article originally appeared on Enterprise Networking Planet, a JupiterWeb site.

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