KDE 4.x

KDE 4.0 is a version of KDE Plasma that was released on 11 January 2008. This version is the first to have the "Oxygen" theme, with new icons, themes, and sounds.

Microsoft Windows support
This version includes experimental Microsoft Windows support, allowing KDE and its apps to run on Windows XP, Vista, and 7. It was later discontinued due to low demand from the community.

Criticism
After its release, it received backlash from the community, especially where performance issues were found and as a result it would perform extremely slow. Due to this, people have either switched to alternate desktop environments or stayed on KDE 3.5. The Trinity Desktop Environment was created in 2010 as a fork of it.

Even despite of this, it lasted as the flagship desktop environment of KDE until it was replaced by KDE Plasma 5 in 2015.