After a wave of operating system releases, it's easy to become somewhat bored with the software side of computing.

Windows 7 is here and looking like the "real" Vista for many; Mac OS X 10.6, meanwhile, adds spit-shine to Leopard and gives its engine a good tuning too. In the Linux camp, distributions are taking regular steps forward in usability.

But it's all become rather routine; a case of incremental improvement rather than revolution. So where's all the real fun happening? Where are the radical new ideas, the Wild West code commits and the geekery and hackery that really drive innovation?

Well, it's all going on in the alternative operating system world. There are hundreds of projects in varying stages of development, from small, one-man-band shows to serious attempts at mounting an assault on the desktop.

We're going to look at 10 of the most intriguing open-source operating systems in this brave new world. In most cases these are available as CD ISO images that you can burn to CD-Rs and boot up for testing if you fancy it.

Alternatively, a simpler approach is to use a PC emulator such as VirtualBox or Qemu. With these and similar tools you can use '.iso' image files (or '.flp' floppy disc images) as virtual drives, so there's no need to write any physical media.

1. ReactOS

Goal: Run Windows apps on an open-source OS

Web: www.reactos.org

Out of all the operating systems we looked at, ReactOS is the one most likely to have Steve Ballmer tossing chairs. Originally named FreeWin95, the developers' original goal was to create a completely open-source clone of, you guessed it, Windows 95.

As time went on, however, there was little serious code to show and it was clear that the NT code base was the future for Microsoft. In 1998, ReactOS rose out of the ashes of FreeWin95.

Early progress was slow, but in 2004 version 0.2.0 arrived with a usable desktop and respectable, albeit very limited, Windows compatibility. Today, ReactOS is based around a home-grown kernel, but the project makes heavy use of the WINE libraries that are popular for running Windows applications on Linux.

ReactOS is available as a Live CD or as an installable OS. Right now, it looks and feels much like Windows 2000. Chunky widgets abound, and the Start menu, taskbar, window buttons and so forth are where you'd expect to see them.

So, is it compatible? Chasing Microsoft's vast APIs is no easy job, especially with so many undocumented calls to fathom out, but ReactOS does an impressive job. Firefox (with Flash), MSN Messenger, OpenOffice.org, StarCraft, Diablo 2, Quake III arena and many more apps run acceptably well, albeit with the occasional crash. Newer versions of MS Office and Visual Basic have troubles, though.

It's an ongoing job. At this point you may be asking: 'Why would Microsoft be worried about an OS that still needs a lot more work?'

Sure, right now ReactOS is no threat to Redmond. But for the tens of millions of people on the planet who use Windows as a springboard for a web browser, word processor and Solitaire, ReactOS could one day be a completely free drop-in replacement. If the project receives commercial backing in the future, Microsoft's response will be interesting to watch.

2. Haiku

Goal: Be a free reincarnation of BeOS

Web: www.haiku-os.org

Sadly, BeOS never made the mainstream desktop impact that its supporters so passionately hoped for. This multimedia-focused operating system peaked in the late 1990s, but Microsoft's stranglehold on the desktop prevented it from attaining anything more than relative obscurity.

Those days are gone, but the spirit of BeOS lives on. Haiku is named after BeOS's error messages, many of which were quaintly fashioned in Japanese poetry format.

Like BeOS, Haiku aims to be compatible with the small range of native BeOS programs. It's available in raw hard drive image format, suitable for Qemu; CD-based versions are due out in the coming months.

Haiku's interface is refreshingly minimal. Window title bars are reduced to small yellow tabs with a single close button, while the leaf button at the top-right of the desktop opens up a pseudo Start menu containing applications and settings. Even in an emulator, it runs at an impressive speed – see how many GLTeaPot demos you can run before the OS starts to stutter.

Even in its pre-alpha state, Haiku is shaping up well, with a wide range of included applications and utilities for desktop usage. When you open up a command line you may be surprised to find the Bash shell, although Haiku is in no way a Unix flavour.

Of all the alternative OSes currently undergoing development, Haiku is the closest to achieving a stable, fully featured 1.0 release, although that day may still be a way off .

3. AROS

Goal: Recreate the glory days of AmigaOS

Web: http://aros.sourceforge.net

Astoundingly, AmigaOS lives on, despite Commodore's bankruptcy 15 years ago. To its fans, the Amiga was revolutionary, offering graphics and sound in the late 1980s that put PCs to shame.

It wasn't without its problems, though: the lack of memory protection resulted in colossal crashes when a single app misbehaved. 'Guru meditation' error messages still haunt the memories of many.

AROS's aim is to provide an lightweight Amiga compatible OS for modern machines, with source code compatibility with AmigaOS 3.1: in other words, if you have the source code for an old Amiga app, you can recompile it to run natively on AROS on an x86 chip.

Many versions of AROS are available, and you can even run it from inside Linux. For the best experience, though, grab the 'pc-i386-boot-iso' CD-R image and boot it.

If you're a former Amiga fan, you'll probably well up when Wanderer, the Workbench replacement, loads up: aside from the modern lick of paint, it feels just like the glory days of AmigaOS. The filesystem layout is the same, right-clicking activates the menu at the top, and in the Extras/Demos folder you'll find heaps of toys.

While AROS is undoubtedly attractive to those who pine after the great days of the Amiga, it's an impressively swift and polished desktop OS in its own right. We don't expect it to become massive overnight, but it'll always have a hardcore army of fans.

4. Aranym

Goal: Keep the Atari ST/TT/Falcon alive

Web: http://aranym.sourceforge.net

Atari ST fans have their own equivalent in Aranym. It's a virtual machine that emulates a 68040 CPU and various Atari hardware components, on top of which sits AFROS, an open-source version of the TOS/GEM operating system.

You can download it as a program that runs on top of your normal operating system, or alternatively grab the Live CD. AFROS is – to be blunt – supremely ugly, but then GEM was never known for its looks. Nevertheless, it's a sprightly performer, and Atari users will have no problem finding their way around.

A Windows-esque program menu has been shoe-horned into the bottom side of the screen, and on the whole it faithfully recreates Atari's 16-bit machines: if you were an Atari fan in the '90s and still have some old floppies lying around, you might be able to get your old apps running.

5. Syllable

Goal: Provide a user-friendly desktop OS

Web: www.syllable.org

Thus far, all of the OSes we've looked at have been based on other OSes. Syllable, however, has been engineered from the ground up as a unique OS, with some inspiration from BeOS and AmigaOS.

Originally known as AtheOS, the project development was forked after the lead developer effectively abandoned his work, and Syllable was born.

After booting from the Live CD, you can log in as the user 'root' with password 'root'. The desktop is playfully colourful and clean: click the 'S' button at the top left to peruse the installed software. T

here's the usual collection of desktop utilities, including a media player and WebKit based browser. It's impressively fast and has the potential to be an excellent desktop OS for breathing new life into older machines.

At version 0.6.6, Syllable is one of the most advanced alternative OSes around. Unfortunately, though, there's a distinct lack of native software, and development on the project has slowed down in the last couple of years.

If you're interested in helping out on an OS project, then Syllable's small but friendly team is a good place to start.