Along with Gnome, KDE is one of the two most widely used desktop environments for Linux and Unix systems. With the KDE 4 series, developers shifted the system from the Qt 3 application-development framework to Qt 4, while rebuilding the desktop environment from scratch.
KDE 4, however, was criticized by users on open-source mailing lists for its lack of features and customization, bugs and usability problems. Some suggested including older versions of KDE alongside KDE 4 or even creating a new system based on KDE 3.5 but ported to the Qt 4 framework.
Developers said that, with version 4.1, a number of additional applications have made the transition to KDE 4, most notably the personal information manager Kontact, which includes the email client KMail, the planner KOrganizer and other components.
Unlike its predecessors, Qt 4 was released for Windows, meaning KDE 4 applications can run natively on that platform. KDE 4 applications also run natively on Linux and Unix variants, including Mac OS X.
Another significant change with KDE 4 was the introduction of an engine for generating desktop and window panels, called Plasma.
"The new desktop shell Plasma, introduced in KDE 4.0, has matured to the point where it can replace the KDE 3 shell for most casual users," developers said in the KDE 4.1 announcement. It now supports multiple and resizable panels, allowing the same flexibility as KDE 3's system, the developers said, adding that it now includes features such as a Cover Switch, as well as performance gains in composited window management.
Other applications now ported to KDE 4 include the Dragon Player media player and the KDE CD Player. Other elements that have been tweaked include the Konqueror browser and the Dolphin file manager.
Developers have improved the speed of KHTML, the browser engine on which Konqueror is based, and have integrated Apple's KHTML-based web-rendering toolkit WebKit into Plasma to allow Mac OS X Dashboard widgets to be used in KDE.
In a recent open letter defending KDE 4, KDE board member Sebastian Kügler said the underlying improvements to the development infrastructure would begin to be more apparent in version 4.1. "The new features and frameworks need some time to be implemented in a user-visible way," he wrote. "The merit of the infrastructural work that has led up to 4.0 will be seen in the coming releases, with KDE 4.1 showing first signs of an increased pace of development, thanks to the new foundations."
The stable binaries and source code are available from KDE's website.