Xen

Xen is a free software virtual machine monitor for IA-32, x86-64, IA-64 and PowerPC architectures. It is software that runs on a host operating system and allows several guest operating systems to be run on top of the host on the same computer hardware at the same time. Modified versions of Linux and NetBSD can be used as hosts. Several modified Unix-like operating systems may be employed as guest systems; on certain hardware, as of Xen version 3.0, unmodified versions of Microsoft Windows and other proprietary operating systems can also be used as guests.

Xen originated as a research project at the University of Cambridge, led by Ian Pratt, senior lecturer at Cambridge and founder of XenSource, Inc. This company now supports the development of the open source project and also sells enterprise versions of the software. The first public release of Xen was made available in 2003. XenSource, Inc was acquired by Citrix Systems in October 2007. XenSource's products have subsequently been renamed under the Citrix brand: XenExpress was renamed "XenServer Express Edition" and "XenServer OEM Edition" (embedded hypervisor); XenServer was renamed "XenServer Standard Edition"; XenEnterprise was renamed "XenServer Enterprise Edition".

Homepage: http://xen.xensource.com

Microsoft Virtual PC

Microsoft Virtual PC is a virtualization suite for Microsoft Windows operating systems, and an emulation suite for Mac OS X on PowerPC-based systems. The software was originally written by Connectix, and was subsequently acquired by Microsoft. In July 2006 Microsoft released the Windows-hosted version as a free product. In August 2006 Microsoft announced the Macintosh-hosted version would not be ported to Intel-based Macintoshes, effectively discontinuing the product as PowerPC-based Macintoshes are no longer manufactured.

Virtual PC emulates a standard PC and its associated hardware. Thus, it can be used to run nearly all operating systems available for the PC. However, issues can arise when trying to install uncommon operating systems that have not been specifically targeted in the development of Virtual PC.

Homepage: http://www.microsoft.com/...

DOS Box

DOSBox is an x86 emulator which creates a DOS-like environment intended for running MS-DOS-based IBM PC compatible programs, especially DOS-bound computer games, which may not run properly on newer PCs and may not run at all on non-IBM PC compatibles (e.g. PowerPC Macintosh). DOSBox is open source and available for many operating systems, such as Linux, OpenBSD, FreeBSD, Windows 9x, Windows NT 4.0, Windows 2000, Windows XP (32-bit and 64-bit), Windows 2003, Windows Vista, Mac OS X, OS/2, Palm OS, RISC OS, and BeOS. It has also been ported to PlayStation Portable and the GP2X device.

DOSBox has been used by software companies to redistribute MS-DOS-native games in a format which can be run on Windows NT-based operating systems. Most recently, Steam interactive has teamed up with id Software to distribute various DOS games such as Wolfenstein 3D and Commander Keen bundled with DOSBox.

Homepage: http://dosbox.sourceforge.net

VMware Player

VMware Player is a freeware virtualization software product from VMware, Inc., a subsidiary of EMC Corporation. Player can run guest virtual machines produced by other VMware products; it cannot itself create new virtual machines. VMware provides free virtual disk images of several pre-configured operating systems and applications, many of them community-contributed. Freeware tools and websites (such as EasyVMX) also exist for creating VMs, mounting, manipulating and converting VMware disks and floppies, permitting users to create, run and maintain virtual machines free of charge (even for commercial use).

VMware Player also forms part of the VMware Workstation distribution, for the purpose of site-wide installations with client users not licensed to use the full VMware Workstation product.

Homepage: http://www.vmware.com/products/player

VMware Server

VMware Server (formerly GSX Server) is an entry-level server virtualization software suite from VMware, Inc., a subsidiary of EMC Corporation. VMware released version 1.0 of Server on July 12, 2006. Server is a continuation of the retired GSX Server product line. VMware Server can create, edit, and play virtual machines. It uses a client-server model, allowing remote access to virtual machines, at the cost of some graphical performance (and 3D support). In addition to the ability to run virtual machines created by other VMware products, it can also run virtual machines created by Microsoft Virtual PC. VMware, Inc. makes Server freely available in the hope that users will eventually upgrade to VMware ESX Server.

Users of VMware Server's internal utilities can preserve (and revert to) a single snapshot copy of each separate virtual machine within their VMware Server environment. The product does not have a specific interface for cloning virtual machines, unlike VMware Workstation.

At present, VMware Server supports only 32-bit editions of Microsoft Windows Vista. The kernel-mode drivers for the 64-bit version do not have digital signatures, so 64-bit editions of Vista prevent their installation.

Homepage: http://www.vmware.com/products/server

VirtualBox

VirtualBox by InnoTek is a commercial and proprietary (with a limited GPL version) x86 virtualizer for Linux, Mac OS X (beta version) and Windows 32-bit and 64-bit hosts supporting FreeBSD, Linux, OpenBSD, OS/2 Warp and Windows as guest operating systems. After several years of development, VirtualBox OSE (Open source edition), a limited, open-source version, was released under the GNU General Public License (GPL) in January 2007.

Compared with the other established commercial virtualization software such as VMware Workstation and Microsoft Virtual PC, VirtualBox lacks some features, but in turn provides others. Such unique features are running virtual machines remotely over the Remote Desktop Protocol (RDP), iSCSI support and USB support with remote devices over RDP.

VirtualBox supports Intel's hardware virtualization VT-x and has experimental support for AMD's AMD-V, but doesn't use either of them by default.

Homepage: http://virtualbox.org