KaOS is a Linux distribution that is built from scratch with a very specific focus on Qt and KDE.

Although KaOS is currently based on the Linux kernel, the developers are "constantly evaluating" the illumos kernel, and say that "a future switch is a wish"

History
The first version of KaOS was released as "KdeOS" in 2013. To prevent confusion between the distribution's name and the desktop environment KDE, the name was changed to "KaOS" in September 2013.

Features
KaOS is distributed via an ISO image, and exclusively supports 64-bit processors.

The idea behind KaOS is to create a tightly integrated rolling and transparent distribution for the modern desktop, build from scratch with a very specific focus. Focus on one DE (KDE Plasma), one toolkit (Qt), one architecture (x86_64) plus a focus on evaluating and selecting the most suitable tools and applications.

Receptions
Phoronix wrote in 2016, "Overall, I was quite pleased with it for being a niche distribution. KaOS was easy to install and was quickly running on a bleeding-edge KDE Plasma 5 stack. Overall, it was a fun and pleasant few hours spent with KaOS.

FossMint stated in 2017, that KaOS "is a modern, open-source, beautifully designed, QT and KDE-focused Linux distro. It is a rolling release that ships with KDE Plasma as its default Desktop Environment, uses Pacman as its package manager, and has a 3-group structure repository on GitHub." and "The fact that it is a rolling release means that you will never need to worry about future updates the moment you have a version installed like in the case of Ubuntu and the like where you would need to consider whether to perform a clean installation of another “major version” or not."