gHacks has already covered ReactOS; a free and open source version of Windows, but there are many other operating systems out there which not many people use.

BeOS was a commercial operating system which died during the dot com crash. It was quite advanced and a number of hobbyists still maintain operating systems based on it. The biggest has to be Haiku, which is still in pre-alpha but now has a GCC4 build, so many more applications will be ported to it. BeOS, and presumably Haiku, are POSIX-compliant although not Unix-based.

MenuetOS is another personal favourite. Unlike Haiku, this is not POSIX or Unix-based. MenuetOS is free for educational use. The operating system has decent networking abilities, a web server, a web browser and a GUI. It even has webcam support! MenuetOS amazingly fits onto a standard floppy diskette despite this! This could be useful for a simple server with minimal demand.

AROS is an operating system based on AmigaOS and is now nearly complete to it. Unlike AmigaOS, AROS works on x86 computers. I haven’t tried it but Wikipedia claims there’s a basic version of the AMosaic web browser for it. The operating system is small too, being about 50MB big.

Have I missed any out?

ReactOS is a free and open-source operating system, which has been in the alpha stage of development for about 10 years, which allows Windows applications and libraries to be executed without having to use a single piece of Microsoft-owned code!

A similar project to ReactOS is WINE, which allows you to execute Windows binaries in Linux and OS X.

ReactOS has an easy-to-use graphical interface, which resembles Windows Classic. Some things, like the Windows logo, are avoided however. It adds some features Windows lacks, such as virtual desktops.

The practical uses of ReactOS are somewhat limited. The operating system can run many Win32 applications, but this is patchy, and support for .NET Framework applications, OpenGL and DirectX is still being developed. Their own website acknowledges that ReactOS is ‘not recommended for everyday use’.

Their website boasts a selection of screenshots of all sort of programs running under ReactOS, for example OpenOffice.org, Mozilla Firefox, VB5, Winamp, Diablo 2 and Unreal Tournament!

ReactOS with a classic Windows game!

The operating system is probably not usable as of yet as someone’s main operating system, but its idea and sheer curiosity value makes it fascinating. When it becomes stable, it will be interesting to see how a completely Win32-compatible operating system fares against Windows XP and Windows Vista.