Aderivative is a distro that is based on the work done in the upstream distro, but has its own identity, goals and audience. Debian, Ubuntu and Fedora are popular options for creating derivatives. There’s a number of distros based on Debian, including several that have gone on to become popular in their own niche, such as the pentesting distro Kali Linux, and the privacy and anonymity distro Tails. The most popular derivative by far, though, is Ubuntu, which has become a key Linux distro in itself.
The default desktop environment of Fedora is Gnome, but if you prefer an alternative desktop such as KDE or Xfce, you can download a spin for your preferred desktop environment. Then there’s Fedora Labs, which is a selection of curated bundles of purpose-driven software and content, such as Security, Games, Astronomy and such. They are curated and maintained by members of the Fedora community, and may be installed as standalone Fedora-based distros.