Virtualization Software

Virtualization software allows a single host computer to create and run one or more virtual environments. Virtualisation software is most often used to emulate a complete computer system in order to allow a guest operating system to be run, for example allowing Linux to run as a guest on top of a PC that is natively running a Microsoft Windows operating system. Storage virtualization refers to the process of abstracting logical storage from physical storage.

Virtualization Software :

1. OpenVZ is an operating system-level virtualization technology based on the Linux kernel and operating system. This is OSS.
2. Xen is a virtual machine monitor for 32 / 64 bit Intel / AMD (IA 64) and PowerPC 970 architectures. It allows several guest operating systems to be executed on the same computer hardware concurrently. XEN is included with most popular Linux distributions such as Debian, Ubuntu, CentOS, RHEL, Fedora and many others. This is OSS too.
3. Linux-VServer is a virtual private server implementation done by adding operating system-level virtualization capabilities to the Linux kernel.This is OSS.
   
4. VirtualBox is an x86 virtualization software package, developed by Sun Microsystems as part of its Sun xVM virtualization platform. Supported host operating systems include Linux, Mac OS X, OS/2 Warp, Windows XP or Vista, and Solaris, while supported guest operating systems include FreeBSD, Linux, OpenBSD, OS/2 Warp, Windows and Solaris. This is OSS.
5. VMware ESX Server and VMWare Server - VMware Server (also known as GSX Server) is an entry-level server virtualization software. VMware ESX Server is an enterprise-level virtualization product providing data center virtualization. It can run various guest operating systems such as FreeBSD, Linux, Solaris, Windows and others. This is proprietary.

S0urce :
Top 10 Linux Virtualization Software
Wikipedia