Quick introduction of all the main things

Linux

Linux is an open-source operating system kernel initially created by Linus Torvalds. It serves as the base kernel for many different operating system distributions (distros).

KDE Plasma

KDE Plasma is an open-source desktop environment used by some Linux distributions.

Red Hat

Red Hat, Inc. is a software company which makes Red Hat Enterprise Linux (RHEL), a commercial Linux distribution.

Fedora

Fedora is a free community-developed Linux distribution which serves as the upstream for RHEL (the code from Fedora is used to make future versions of RHEL). Some Red Hat employees work on Fedora and Red Hat is Fedora's largest sponsor. Around 35% of the people contributing to Fedora work at Red Hat.

Fedora Atomic Desktops

Atomic desktops are a new way to deploy Linux which delivers OS updates in the form of immutable images. It is designed to make updating more reliable and reduce the chance of the OS being bricked by a bad update. See also Atomic Desktops introduction.

Universal Blue

Universal Blue is a community-driven project to build custom immutable operating system images based on Fedora Atomic Desktops. Their OS images essentially bundle Fedora with various enhancements.

Aurora and Bluefun

Aurora and Bluefin are Fedora images from Universal Blue which are oriented towards developers. Aurora uses the KDE Plasma desktop environment. Bluefun uses GNOME.

Bazzite

Bazzite is a Fedora image from Universal Blue which is oriented towards gamers. It comes with things like Steam, Lutris, ProtonPlus, gamescope etc preinstalled. There is a variant for handhelds which provides SteamOS-like features such as the Steam Deck Gaming Mode. Desktop environment is KDE Plasma.