MS DOS

MS-DOS (short for Microsoft Disk Operating System) is an operating system commercialised by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the dominant operating system for the PC compatible platform during the 1980s. It has gradually been replaced on consumer desktop computers by various generations of the Windows operating system.
MS-DOS was originally released in 1981 and had eight major versions released before Microsoft stopped development in 2000. It was the key product in Microsoft's growth from a programming languages company to a diverse software development firm, providing the company with essential revenue and marketing resources. It also provided the platform on which early versions of Windows ran.

windows Vista

Windows Vista contains hundreds of new and reworked features; some of the most significant include an updated graphical user interface and visual style dubbed Windows Aero, improved searching features, new multimedia creation tools such as Windows DVD Maker, and completely redesigned networking, audio, print, and display sub-systems. Vista also aims to increase the level of communication between machines on a home network using peer-to-peer technology, making it easier to share files and digital media between computers and devices. For developers, Vista includes version 3.0 of the .NET Framework, which aims to make it significantly easier for developers to write applications than with the traditional Windows API.

windows Me

Windows Me is not a new Windows version; the user interface makes the program look like Windows 2000, but "under the hood" it's still Windows 9x code.
New in Windows Me are:
System Restore function
A new TCP/IP stack
Windows Media Player 7
Internet Explorer 5.5
Movie Maker application for recording, editing, publishing, and organizing audio and video content
No Real mode DOS

OS/2

The Window List displays a list of open windows that you can select. In Os/2 minimized windows DISAPPEAR instead of float to the bottom of the screen by default and you would need to use the Window List to retrieve it.
The OS/2 desktop can also create shortcuts to items, except here they are referred to as "shadows" (and are actually more advanced, more like MacOS aliases).

Mac OS

Mac OS X (pronounced /mæk.oʊ.ɛs.tɛn/) is a line of graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. Mac OS X is the successor to the original Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessors, Mac OS X is a Unix-based operating system[1] built on technology that had been developed at NeXT through the second half of the 1980s until Apple purchased the company in early 1997.
The first version released was Mac OS X Server 1.0 in 1999, and a desktop-oriented version, Mac OS X v10.0 followed in March 2001. Since then, five more distinct "end-user" and "server" versions have been released, most recently Mac OS X v10.5 in October 2007. Releases of Mac OS X are named after big cats, for example Mac OS X v10.5 is usually referred to by Apple and users as "Leopard".

Linux

Linux can be as useful on the desktop as Windows operating system and at the same time far more stable and secure. This is because of the Linux programs written by the companies and free software programmers all around the world and shared with the users under the liberal GNU/GPL license

windows 2000

Windows 2000 (also referred to as Win2K) is a preemptive, interruptible, graphical and business-oriented operating system designed to work with either uniprocessor or symmetric multi-processor computers. It is part of the Microsoft Windows NT line of operating systems and was released on February 17, 2000. It was succeeded by Windows XP in October 2001 and Windows Server 2003 in April 2003. Windows 2000 is classified as a hybrid kernel operating system.
Windows 2000 was made available in four editions: Professional, Server, Advanced Server, and Datacenter Server. Additionally, Microsoft offered Windows 2000 Advanced Server Limited Edition and Windows 2000 Datacenter Server Limited Edition, which were released in 2001 and run on 64-bit Intel Itanium microprocessors.[4] Whilst all editions of Windows 2000 are targeted to different markets, they each share a core set of common functionality, including many system utilities such as the Microsoft Management Console and standard system administration applications. Support for people with disabilities was improved over Windows NT 4.0 with a number of new assistive technologies, and Microsoft included increased support for different languages and locale information. All versions of the operating system support the Windows NT filesystem, NTFS 3.0,[5] the Encrypting File System, as well as basic and dynamic disk storage.