KDE (K Desktop Environment) (IPA: /ˌkeɪˌdiːˈiː/) is a free software project which aims to be a powerful system for an easy-to-use desktop environment. The goal of the project is to give basic desktop functions and applications for daily needs as well as tools and documentation for developers to write stand-alone applications for the system. In this regard the KDE project serves as an umbrella project for many standalone applications and smaller projects that are based on KDE technology. These consist of KOffice, KDevelop, Amarok, K3b and many others.

History

KDE was founded in 1996 by Matthias Ettrich, who was then a student at the Eberhard Karls University of Tübingen. At the time, he was troubled by certain aspects of the UNIX desktop. Among his qualms was that none of the applications looked, felt, or worked alike. He proposed the formation of not only a set of applications, but rather a desktop environment, in which users could expect things to look, feel, and work consistently. He also wanted to make this desktop easy to use; one of his complaints with desktop applications of the time was that his girlfriend could not use them. His initial Usenet post spurred a lot of interest, and the KDE project was born. The name KDE was intended as a word play on the existing Common Desktop Environment, available for Unix systems. CDE was an X11-based user environment jointly developed by HP, IBM, and Sun, through the X/Open Company, with an interface and productivity tools based on the Motif graphical widget toolkit. It was supposed to be an intuitively easy-to-use desktop computer environment. The K was originally suggested to stand for "Kool", but it was quickly decided that the K should stand for nothing in particular. Additionally, one of the tips in certain versions of KDE 3 incorrectly states that the K currently is just meant to be the letter before L in the Latin alphabet, the first letter in the word Linux (which is where KDE is typically run).

Matthias chose to use the Qt toolkit for the KDE project. Other programmers quickly started developing KDE/Qt applications, and by early 1997, large and complex applications were being released. At the time, Qt did not use a free software license and members of the GNU project became concerned about the use of such a toolkit for building a free software desktop and applications. Notably, KDE was removed from Debian because the project interpreted the GPL as not allowing KDE to be linked to Qt. Two projects were started: "Harmony", to create a Free replacement for the Qt libraries, and the GNOME project to create a new desktop without Qt and built completely on top of free software.

In November 1998, the Qt toolkit was licensed under the free/open source Q Public License (QPL). The same year, the KDE Free Qt foundation was created which guarantees that Qt would fall under a variant of the very liberal BSD license should Trolltech cease to exist or no free/open source version of Qt be released during 12 months. Debate continued about compatibility with the GNU General Public License (GPL), so in September 2000, Trolltech made the Unix version of the Qt libraries available under the GPL, in addition to the QPL, which eliminated the concerns of the Free Software Foundation. Qt 4.0 is available under the GPL for the Unix, Mac and Windows platforms, enabling KDE 4 applications and libraries to have native support on all these platforms.

Both KDE and GNOME now participate in freedesktop.org, an effort to standardize Unix desktop interoperability, although there is still some competition between them.

Release cycle and version numbers

A screenshot of KDE 3.5 running the Kontact personal information manager and Konqueror file manager

The KDE team releases new versions on a regular basis. There are two main types of releases, major releases and minor releases.

Major releases

Major releases contain new features. There have been 12 major releases so far - the current major release is 4.0, which arrived on January 11, 2008.

As soon as a major release is ready and announced, work on the next major release starts. A major release needs several months to be finished and many bugs that are fixed during this time are backported to the stable branch, meaning that these fixes are incorporated into the last stable release.

X.0 releases

The KDE X.0 releases are special, as they are allowed to break both binary and source-compatibility with the predecessor, or to put it differently, all following releases (X.1, X.2, …) will guarantee binary (ABI) and source compatibility (API). This means, for instance, that software that was developed for KDE 3.0 will work on all (future) KDE 3 releases, in contrast to an application that was developed for KDE 2, which is not guaranteed to be able to make use of the KDE 3 libraries.

The changes between KDE 1 and KDE 2 series were large and many, while the API changes between KDE 2 and KDE 3 were comparatively minor. There have been major changes between KDE 3 and KDE 4. KDE major version numbers follow the Qt release cycle meaning that KDE 4 is based on Qt 4, while KDE 3 was based on Qt 3.

Minor releases

A minor KDE release has three version numbers, e.g. KDE 1.1.1, and a centre on fixing bugs, minor glitches and making small usability improvements. Minor releases in general do not allow new features although some releases in the 3.5.x line have had minor enhancements. For minor releases, a shortened release schedule is used.

Timeline of major releases

For more details on this topic, see Timeline of KDE development.

Organization

Like many free/open source software projects, KDE is primarily a volunteer effort, although various companies, such as Novell (in the form of SuSE), Trolltech, and Mandriva employ developers to work on the project. Since a large number of individuals contribute to KDE in various ways (e.g. code, translation, artwork), organization of such a project is complex. Most problems are discussed on a number of different mailing lists.

Important decisions, such as release dates and inclusion of new applications, are made on the kde-core-devel list by the so-called core developers. These are developers who have made significant contributions to KDE over a long period of time. Decisions are not made by a formal voting process, but by discussion on the mailing lists. In most cases this seems to work well, and major debates (such as the question of whether the KDE 2 API should be broken in favour of KDE 3) are rare.

While developers and users are now located all over the world, the project retains a strong base in Germany. The web servers are located at the universities of Tübingen and Kaiserslautern, a German non-profit organization (KDE e.V.) owns the trademark on "KDE", and KDE conferences often take place in Germany.

Development

Architecture

KDE is built with Trolltech's Qt toolkit which runs on most Unix and Unix-like systems, Mac OS X and Microsoft Windows. All releases of KDE 3 are built upon Qt 3, which was only released under the GPL for Linux and Unix-like operating systems, including Mac OS X. For that reason, KDE 3 is only available on Windows through ports involving an X server.

KDE 4 is based on Qt 4 which is also released under the GPL for Windows and Mac OS X. Therefore KDE 4 applications can run natively on these operating systems as well.

Usability

KDE aims to make easy-to-use programs without sacrificing features. KDE's Usability page states its goal as: "Working within the existing design goals of a system, usability efforts aim to make the implementations of these designs easier to use, faster to learn, more consistent and obvious, and typically more ergonomic for their target audience." To improve the user interface, work has gone into reducing visual complexity for versions 3.2 to 3.5. The most promising effort is the close work with the OpenUsability Project. One of the major goals of KDE 4.0 is to identify further areas that are lacking from a usability perspective and address these concerns. In particular, new human interface guidelines are being developed for KDE 4.0.

KDE strives to make otherwise onerous or difficult tasks easier, such as adding printers (local or networked), setting up 802.11 Wireless security settings (such as WEP), and installing new fonts and window decorations. Third-party web sites LinuxPrinting, art4linux.org and KDE-Look support KDE through adding devices or customizing the environment's look and feel.

The KDE interface has been criticised for being too complex and including too many configurable options. However, a usability report evaluating a customized version of KDE 3.1 showed, as early as 2003, that Windows users quickly became familiar with KDE, enjoyed it and were able to accomplish the proposed task as quickly as with Windows XP.

Major KDE applications

For a full list, see list of KDE applications. Applications for KDE include:

Amarok - Audio player

Akregator - Aggregator

K3b - Optical disc authoring software

Kate - Text editor

KDevelop - Integrated Development Environment (IDE)

KMail - E-mail client

KNode - News client

Konsole - Terminal emulator

Kontact - E-mail client, News client, Aggregator, Personal Information Manager, Todo lists and more.

Kopete - Instant messaging client

Konqueror - File manager and web browser

KWord - Word processor

KWrite - Lightweight text editor

Base technologies used in KDE

KDELibs

KHTML - HTML engine

KIO - extensible network-transparent file access

Kiosk - allows disabling features within KDE to create a more controlled environment

KParts - lightweight in-process graphical component framework

KWin - window manager

XMLGUI - allows defining UI elements such as menus and toolbars via XML files

Technologies added in KDE 4

Plasma - desktop and panel widget engine

Phonon - multimedia framework

Solid - device integration framework

Sonnet - spell checker

ThreadWeaver - library to more effectively utilize multiprocessor systems

Technologies superseded in KDE 4

aRts - sound server (replaced with Phonon)

DCOP - inter-process communication system (replaced with D-Bus)

Packaging

Due to the size of KDE, it is divided into several package categories to simplify installation. This is a reference scheme; packagers are free to use their own packages for KDE.

aRts - KDE sound server.

KDELibs - Primary libraries, containing most pieces of KDE architecture

Kdebase - The base desktop and applications. Requires kdelibs.

Kdeaccessibility - Accessibility software

Kdeaddons - Add-on software

Kdeadmin - Administrative tools, intended for administering UNIX machines

Kdeartwork - Additional artwork (widget style, screensavers, wallpapers, etc.)

Kdeedu - Educational software

Kdegames - Games

Kdegraphics - Tools for manipulating graphics

Kde-i18n - Internationalization for KDE

Kdemultimedia - Multimedia software

Kdenetwork - Network tools and software

Kdepim - Personal information management and E-mail software

Kdesdk - Developer tools

Kdetoys - Desktop toys and amusements

Kdeutils - Utilities

Kdewebdev - Web development

KOffice - Office suite

Kdebindings - Support for other programming languages

There is also a Subversion module, Extragear, which is used by applications which are part of the KDE project but do not follow the release cycle of the main codebase; K3b and Amarok are part of this module.

KDE 4

Main article: KDE 4

KDE 4, the current series of KDE releases, is a major revision of KDE, based on the version 4 series of Qt. KDE 4.0 was released on January 11, 2008.

Some of the new features are:

A new default look and feel, called Oxygen, and 3D effects in the KWin window manager.

A completely redesigned desktop and panels collectively called Plasma which integrates Kicker, KDesktop, and SuperKaramba and is intended to update the decades-old desktop metaphor.

A new multimedia interface (Phonon), making KDE independent of any one specific media framework.

An API for network and portable devices (Solid)

A new communication framework (Decibel)

A metadata and search framework, probably named Tenor. It incorporates Strigi as a full-text file indexing service, and NEPOMUK with KDE integration.

A new default file manager (Dolphin)

Microsoft Windows and Mac OS X support by KDE libraries so that KDE applications will more easily be ported to these operating systems.

A new spell checking program called Sonnet with automatic language detection. It replaces Kspell to mark misspellings in text input fields in KDE-based applications. Advantages over Kspell are the automatic language detection and the ability to work even if several languages are mixed in one document.

Licensing issues

Qt, to which native graphical KDE applications link for their graphical widgets, is free software, dual-licensed under the GNU GPL and QPL licenses. TrollTech also sell licenses for developing proprietary software. When using the free versions, programs which link to Qt must be released as FOSS (under the GPL or another license permitted by the QPL, such as the BSD or LGPL for example). After the release of Qt under the GPL, the controversy over licensing with the Free Software Foundation ended.

Some developers of proprietary/closed source software argue that paying for a license, similar to the comparatively expensive development tools of other systems, removes most of the financial incentive for writing proprietary/closed source, native graphical KDE applications. However, it is not necessary to use Qt or the KDE libraries to write software which integrates well with the KDE desktop. Software using any other toolkit, following the freedesktop.org standards or using KDE facilities such as KPrinter and KDialog can integrate nicely with the KDE desktop (both KPrinter and KDialog link to Qt, and are under the GPL), however the widgets will not have the exact behavior of Qt widgets. Additional integration efforts are being discussed in the Portland Free Desktop initiative, and are planned for KDE 4.

Some other free/open source desktop platforms (such as GNOME, Xfce and EDE) use toolkits licensed under the LGPL. The LGPL permits proprietary/closed source applications to link to libraries licensed under the LGPL, with some restrictions: the Section 6 of the LGPL v2.1 prohibits linking to software with a license that restricts reverse-engineering and modification of the work for the customer's own use. The proprietary Qt license which Trolltech sells does not carry these restrictions.

Identity

Konqi, mascot of the KDE project

Many KDE applications have a K in the name, mostly as an initial letter and capitalized. However, there are notable exceptions like kynaptic, whose K is not capitalized, and Amarok which formerly had its final k capitalized. The K in many KDE applications is obtained by spelling a word which originally begins with C or Q differently, for example Konsole (which, incidentally, is correct spelling in German) and Kuickshow. Also, some just prefix a frequently used word with a K, for instance KOffice. Some applications do not have a K in the name at all, such as Gwenview. This seems to be an increasing trend among KDE 4 applications and technologies.

The KDE project's mascot is a green dragon named Konqi.

Sponsorship

The KDE project and related events are frequently sponsored by individuals, universities, and businesses.

On 15 October 2006, it was announced that Mark Shuttleworth became the first patron of KDE, the highest level of sponsorship available. On 2007-07-07, it was announced that Intel Corporation and Novell became patrons of KDE.