Poll: Best Free Virtualization Programs

Small to mid-scale virtualization can be done pretty cheaply in today's technology ecosystem.  There are many free and open source solutions that are perfect for tasks such as configuring a reusable development environment, or just basic personal use.  

Virtualization methods can range from partial virtualization, to full virtualization, hardware assisted virtualization, para-virtualization, or operating system-level virtualization.  In my last virtualization poll, I did a survey of various well-known commercial virtualization platforms.  Here are the results so far:



I have since changed VMware vSphere to VMware ESX because this is the more basic commercial solution, whereas vSphere is more cloud oriented.  I also added Oracle VM Server (a commercial solution).  If this changes your answer in that poll, it's easy to go back and change it.  If you think I should add vSphere as well, let me know in the comments of that last poll.

Most of the options in this poll are open source and some are what you might call "bare-metal," but all are freeware.

Which virtualization solution is most appealing to you?