KDE 4 on Windows
The desktop shell in KDE 4 on Linux is provided by Plasma, a flexible, integrated replacement for the separate desktop, widget and taskbar applications of KDE 3. It is possible to run Plasma as the desktop shell on Windows, but some major features are missing—such as a taskbar—and you need to make some changes to the Windows Registry to try it out. In fact, trying Plasma on Windows really is not a good idea on any machine that you care about, because once you have made the switch, you cannot easily revert it from within your KDE Plasma desktop session. The safest way to try Plasma on Windows is to use a new (and disposable) user account in Windows running in a virtual machine. If you do try it (see the Replacing the Windows Desktop Shell with KDE's Plasma sidebar for instructions), you'll be presented with a pretty KDE desktop (Figure 10) to which you can add a few of your favorite widgets, such as a clock or the KDE menu, run a few KDE applications and, well, that's about it. Windows programs are entirely inaccessible. Although there is a certain wow factor to having an almost complete KDE 4 desktop on your Windows machine, using it is not really practical in any serious way at present.
Replacing the Windows Desktop Shell with KDE's Plasma
First, this is a really bad idea and may make your Windows system unusable. If you must follow these instructions, use at least a spare user account and preferably a disposable install in a virtual machine. You have been warned.
If that has not put you off and you still want to see how Plasma looks on Windows, you need to download and run Autoruns for Windows from Microsoft (technet.microsoft.com/en-us/sysinternals/bb963902.aspx).
Next, simply unzip the downloaded archive and run autoruns.exe (not autorunsc.exe).
In the main program window that appears, you then have to select the Logon tab and find the entry that references explorer.exe. Double-click on that to open the registry editor and change the key to replace explorer.exe with the full path to plasma-desktop.exe (if you accepted the default KDE install options, this is probably C:\Program Files\KDE\bin\plasma-desktop.exe).
Log out and back in again. You should be presented with a pretty but largely nonfunctional Plasma desktop.
You'll probably have to press the computer reset button to escape.
Some of the KDE applications are competing for your attention against better-known alternatives that you easily can install from a single executable file. KDE's Konqueror Web browser, although a fine application, finds itself in a very crowded market for Windows browsers with Internet Explorer already installed and the likes of Firefox, Opera, Safari and Google Chrome all available as alternatives. The potential for some other applications to become popular on Windows is, however, much higher. Kopete faces only Pidgin and the proprietary Trillian messenger as serious competition in the market for multiprotocol messaging clients. Okular is a lightweight but well featured alternative to Adobe Reader. Marble is almost in a class of its own—the nearest competitor perhaps being Google Earth. Kontact, the Personal Information Management suite, also has potential as a compelling cross-platform alternative to existing solutions (Figure 11). Mozilla Thunderbird is a clear competitor, but it lacks comprehensive calendar functionality. Benjamin Dietrich, working in IT support at a German university, who currently has to support many different mail applications across the various computing platforms, believes Kontact could “provide one solution, once it is as mature as it is on Linux”. However, a way to distribute Kontact as a self-contained installer easily would add to its appeal: “a single binary installer would be perfect.”
The spread of KDE applications to Windows also has had benefits for the wider KDE Project. Amarok's integration with the Last.fm music service was largely put together by a developer who used Windows rather than Linux. It is unlikely that he would have become involved if it had not been possible at the time to run Amarok on Windows. Getting exposure to users on Windows also gives KDE the potential to attract users to trying KDE 4 on Linux and should make the transition for such users easier if they already know some of the applications.