There are many operating system that needed to use by a developer or end user for testing purpose and application compatibility, the only solution is using virtual machines. Virtual machines can support many operating system such as Windows (NT 4.0, 2000, XP, Server 2003, Vista, Windows 7), DOS/Windows 3.x, Linux (2.4 and 2.6), Solaris and OpenSolaris, OpenBSD and MAC OS. Besides that, Virtual machines also need to be installed in the compatibility operating system before it can be used.

Here introduced some Freeware and Shareware Virtual Machines that compatibility to Windows, Linux and MAC OS.

Windows (FREE)

Microsoft Virtual PC

Microsoft Virtual PC is developed by Microsoft for Windows users. Virtual PC come with some features such as folder integration between host and guest, USB support, Clipboard Sharing, printer redirection and seamless applications. You can access My Documents files such as Videos, Musics, Pictures and Desktop in virtual machine. Besides that, you also can drag mouse out of virtual machine to host without pressing any key as after you install Virtual Machine Additions. Virtual PC can only support All Microsoft Windows products ifit can support other operating system, please remind me for changes.

VirtualBox

VirtualBox is developed by Sun Microsystems. VirtualBox can only support few operating system such as almost all Microsoft Windows, Linux, Solaris and OpenBSD. Some of the features are same with Microsoft Virtual PC. A number extra features are available in full VirtualBox only. VirtualBox has an extremely modular design with well-defined internal programming interfaces and a client/server design. Other than that, VirtualBox also allowed full support of Remote Desktop Protocol.

VMware Player

VMware Player is VMware Inc. VMware Player is free software that enables users to easily run any virtual machine on a Windows or Linux PC. VMware Player runs virtual machines created by VMware Workstation, VMware Server, or VMware ESX and also supports Microsoft virtual machines and Symantec LiveState Recovery disk formats.

Windows (Shareware)

VMware Workstation

VMware Workstation as mention above is the software that can create Virtual disk while VMware player that enable users to configure their machines for optimal performance as well as access host PC devices. VMware Workstation support many operating system such as Microsoft Windows, Linux, OpenBSD and MAC OS(with specific settings). VMware Inc. also offer VMware vCenter Server for corporation used such as server hosting, web hosting or files hosting. The price of VMware Workstation is USD$189.00.

Parallels Workstation

Parallels Workstation is a powerful and easy-to-use virtualization software for Windows and Linux designed to work with a wide range of operation systems. Parallels Workstation helps enterprises and individuals worldwide use virtual PCs to move from a traditional physical IT infrastructure to a virtual one. Parallels Workstation virtual machine profiles can be easily zipped in a single file that can be instantly loaded on any Parallels Workstation-enabled machine. The price of Parallels Workstation is USD$49.99

Linux (FREE)

Kernel Based Virtual Machine (KVM)

KVM is a full virtualization solution for Linux on x86 hardware containing virtualization extensions. It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko. KVM also requires a modified QEMU although work is underway to get the required changes upstream. KVM support many operating system such as Microsoft Windows, Linux, OpenBSD, Solaris and many more.

VirtualBox

VirtualBox also can be installed in Linux and support many operating systems. Both of Windows and Linux have the same features.

Linux (Shareware)

VMware Workstation

VMware Workstation also can be installed in Linux and support many operating systems. Both of Windows and Linux Workstation have the same features. The price for VMware Workstation for Linux is USD$189.00.

Parallels Workstation

Parallels Workstation also can be installed in Linux and support many operating systems. Both of WIndows and Linux Workstation have the same features. The price for Parallels Workstation for Linux is USD$49.99.

MAC OS (FREE)

VirtualBox

VirtualBox also can be installed in MAC and support many operating systems. Both of Windows, Linux and MAC have the same features.

MAC OS (Shareware)

VMware Fusion

Vmware Fusion is same features with VMWare Workstation just VMware Fusion can only be install in MAC. The price are more cheaper than VMware workstation that is USD$79.99.

Parallels Desktop

Parallels Desktop is the virtual machine software in MAC. It can support many operating systems. Parallels Desktop 4.0 for Mac is the latest major update of Parallels Desktop for Mac, the market-leading product that enables more than 1.5 million users to run Windows, Linux and other operating systems side-by-side with Mac OS X. The new version of the multi-award-winning Parallels Desktop for Mac performs 50% faster and incorporates a range of security, back up, power saving and OS integration features to give Mac users an easy, fast and powerful way to run Windows on Mac OS X. The price for Parallels Workstation for Linux is USD$79.99.

If you have any other Virtual Machines no matter freeware or shareware, you can share it out in comments.