Open source virtualization offerings are

1. KVM

Short for Kernel-based Virtual Machine, KVM is not as widely deployed as other open source hypervisors, but its stature is growing rapidly. KVM is a full virtualisation hypervisor and can run both Windows and Linux guests. With the kernel component of KVM included in Linux since kernel 2.6.20, KVM can claim a good level of integration with the rest of the operating system.

KVM received its biggest validation in late 2008 when Linux vendor Red Hat acquired KVM developer, Qumranet. Red Hat now bases its enterprise virtualisation server on the KVM hypervisor.

URL: https://www.linux-kvm.org
Licence: GPL

2. Xen

Xen began life as a Microsoft-funded startup at the University of Cambridge and has risen to become the “de facto standard” in Linux hypervisors. Xen supports paravirtualisation and “hardware assisted” virtualisation for modified and un-modified guests, respectively. Guests can be Linux or Windows, but the overwhelming majority of guests are Linux variants, particularly in the hosting space.

A few years ago quite a few commercial software vendors, including Novell and Oracle, adopted Xen and then – seemingly out of nowhere – the commercial startup behind Xen, XenSource, was acquired by Citrix. Citrix has been Xen-happy ever since.

URL: https://www.xen.org
Licence: GPL

3. OpenVZ

OpenVZ is container-based virtualisation for Linux, which has become quite popular among the mass-market Linux hosting providers as an inexpensive way to provide virtual private servers. The OpenVZ containers provides the same services as a separate host and claims to provide near native performance. OpenVZ is the core within Parallels Virtuozzo Containers, a commercial virtualisation solution offered by Swiss company Parallels. Commercial support is available for Parallels. Not a lot has been written about OpenVZ/Parallels in the enterprise space, but there are quite a few glowing user testimonials about the product.

URL: https://openvz.org
Licence: GPL

4. VirtualBox

VirtualBox is an open source desktop virtualisation tool originally developed by German company, innotek, which was acquired by Sun Microsystems in February 2008. Since acquiring Sun, Oracle has continued VirtualBox development and the latest version, 4.0, was released in December 2010. VirtualBox runs on Windows, Linux, Solaris and Mac OS X and can support all those operating systems as guests. While it is mostly used on desktops, VirtualBox is a full virtualisation app and can be used on servers as well. The closed-source edition of VirtualBox is now distributed as an “extension pack” and includes features like RDP and USB support.

URL: https://www.virtualbox.org
Licence: GPL & CDDL

5. Lguest

Lguest is an interesting virtualisation project started by Australian developer, Paul “Rusty” Russell. Designed with Linux in mind, lguest allows multiple copies of the same kernel to run alongside each other.

While not a full virtualisation hypervisor, lguest prides itself on ease of use and uses the same kernel image for host and guest operating systems. There’s not much information about whether lguest is being used in a business production environments, but that would be interesting.

URL: https://lguest.ozlabs.org/
Licence: GPL