KDE (K Desktop Environment) is a Qt-based desktop environment as well as a suite of cross-platform desktop applications. Its latest desktop environment is KDE Plasma 5.
Screenshot of KDE Plasma 4:
KDE is a well-known Qt-based desktop environment, that comes with its own suite of application software.
Key Features
Highly customizable
The range of options is just incredible. It can use a traditional task bar, a unity-like dock, any number of panels.
Very easily modifiable
To get new wallpapers, widgets or themes one can go under System Settings and press the "Get more" button, a dialogue will pop up and all that you need to do is press the "install" button, that it.
Widgets
They can be used on the desktop or in the panel.
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A way to organize your workspaces based on activities.
System Requirements
Required
- Processor - 1GHz (x86)
- Memory - 512 MB
- HDD capacity - 4 GB
- Video Card - VGA @ 640x480
Recommended
- Processor - Better that 1 GHz (x86)
- Memory - 1 GB
- HDD capacity - 10 GB
- Video card - VGA @ 1024x768
Note: If "Desktop effects" are desired, a supported GPU is required.
How to install
Click this link to install the KDE 
Desktop Environment, find it in the Ubuntu Software Center, or type sudo apt-get install kubuntu-desktop in a terminal. There are more instructions here
Alternatively, one can install it from the official image (.iso) that can be downloaded at this page.
Sources
- https://en.wikipedia.org/wiki/Kubuntu#System_requirements
- https://help.ubuntu.com/community/Installation/SystemRequirements
- http://kde.org/info/
