Qt, the GUI toolkit used to create KDE applications was originally not under a completely free software license as Trolltech also had a commercial arm. The main consequences of this were that proprietary programs created for KDE required a license from Trolltech, the creators of Qt, and any upgrades to Qt had to go through Trolltech. As KDE software is an open-source project, the choice to use Qt created controversy among open-source purists. Qt has been re-licensed under the GPL and these arguments have become obsolete, but remain an important part of KDE's history.
To tackle this problem, the KDE Free Qt Foundation was founded by the KDE project and Trolltech. This foundation ensured the continued availability of Qt as a free software development framework. Namely, should Trolltech no longer make Qt available for free software, the currently released version will be re-released under the BSD style license - a license similar in nature but less restrictive than the GPL or LGPL.
This decision to re-release would be moderated by a team of 2 members representing the KDE foundation (unaffiliated with Trolltech) and 2 members from Trolltech to vote. In case of a tie, the KDE vote will gain higher weighting.
Those who prioritised the release of an GPL licensed formed the Harmony project - a project to clone Qt under a GPL license. Rapid progress was made during its time and thus gave purists no excuse to reject KDE as a respectable and compliant desktop environment. However this project was depreciated as Trolltech made the decision to re-license Qt under the GPL.
12 July 1998 - KDE 1.0 Announcement "An integrated Desktop Environment for the Unix Operating System. We are pleased to announce the availability of release 1.0 of the KDesktop Environment"
23 October 2000 - KDE 2.0 released "The KDE Team today announced the release of KDE 2.0, KDE's powerful, modular, Internet-enabled desktop. This highly anticipated release constitutes the next generation of the award-winning KDE 1 series, which culminated in the release of KDE 1.1.2 just over a year ago. KDE 2.0 is the work product of hundreds of dedicated developers originating from over 30 countries. "
17 December 2001 - KOffice 1.1.1 Released "Currently KOffice has functionality well-suited for home and SOHO users, who generally write letters, faxes, memos and similar documents. KOffice 1.1.1 is a minor update release for KOffice 1.1."
3 April 2002 - KDE 3.0 Released "KDE 3.0 is a major step for the KDE project. A hundred words could be written here, but to stop boring you with details, lets just say: Check it out!"
11th May 2007 - KDE 4.0 Alpha 1 Released "KDE Project Ships First Alpha Release for Leading Free Software Desktop."
16th October 2007 - KDE 3.5.8 Released "Project Ships Eighth Translation and Service Release for Leading Free Software Desktop."
11th January 2008 - KDE 4.0 Released "KDE Community Ships Fourth Major Version for Leading Free Software Desktop."
19th February 2008 - KDE 3.5.9 Released "KDE Community Ships Ninth Maintenance Update for Third Major Version for Leading Free Software Desktop."
29th July 2008 - KDE 4.1 Released "KDE Community Ships Major Update to Leading Free Software Desktop."
26th August 2008 - KDE 3.5.10 Released "KDE Community Ships Tenth Maintenance Update for Third Major Version for Leading Free Software Desktop."
12th October 2008 - KDE Forum Launched "KDE Launches Web-based Bulletin Board."
27th January 2009 - KDE 4.2.0 Released "KDE Community Ships Second Major Update To Leading Free Software Desktop."
4th August 2009 - KDE 4.3.0 Released "KDE Community Ships Third Update to the KDE 4 Desktop, Applications and Platform."
9th February 2010 - KDE SC 4.4.0 Released "KDE announces the immediate availability of the KDE Software Compilation 4.4, "Caikaku", bringing an innovative collection of applications to Free Software users."
10th August, 2010 - KDE 4.5.0 released Focusing on "stability, the overall polish and performance gain".
26th January 2011 - KDE SC 4.6.0 Released Major updates to the KDE Plasma workspaces, KDE Applications and KDE Platform
27th July 2011 - KDE 4.7.0 released Containing compelling new features and improvements to the Plasma Workspaces, the KDE Applications and the KDE Development Platform
9th October 2011 - Plasma Active One Arrived First KDE version of cross-device UX.
14th December 2011 - Plasma Active Two Released Second version of cross-Device UX, boosting performance and adding new features.
25th January 2012 - KDE 4.8 Released Gaining adaptive power management, offering faster and more scalable file management, enhancing interoperability and introducing touch-friendly components.
1st August 2012 - KDE 4.9 Released Providing many new features, along with improved stability and performance. Dedicated to the memory of KDE contributor Claire Lotion.
15th October 2012 - Plasma Active 3 Released Improving performance and bringing new applications.
6th February 2013 - KDE 4.10 Released Improving mobile device support, opening up more APIs to Qt Quick and improving performance and usability.
14th August 2013 - KDE 4.11 Released Refined user experience, PIM improvements, better performance.
5th September 2013 - Plasma Active 4 Released Improving overall performance and usability.
18th December 2013 - KDE Applications and Development Platforms Released Bring Huge Step Forward in Personal Information Management and Improvements All Over.
For a more detailed look at the history, including details of all the KDE 3.x releases, see this page