Fedora and Red Hat Enterprise Linux (RHEL) are the most influential distributions that use the Red Hat Package Manager. Although their influence lags behind that of Debian and Ubuntu, it is still strong enough that Fedora remains consistently in the top three most downloaded distributions on Distrowatch, and is the ultimate source of 50 (15%) of the 323 active distributions listed.
Fedora, the successor to Red Hat Linux and perhaps the most influential distribution prior to 2000, is consciously produced as the source for other distributions. In many of its releases, it is among the most innovative distros, releasing new software developed in co-operation with upstream projects. Development is more or less continuous within its Rawhide repository, with stable releases produced every six months.
The main derivative of Fedora is RHEL. RHEL is essentially a snapshot of Fedora, with extra testing for stability and quality control, and the addition of backports of some applications released by Fedora after the snapshot. Since Fedora installs with SE Linux for security, the result is a distribution well-suited to server installations.
However, RHEL is only the start of Fedora's influence. Just as Ubuntu has supported the development of sub-projects like Kubuntu and Xubuntu, so Fedora has encouraged spins and remixes -- customized releases of Fedora designed for specialized purposes.
Moreover, directly and through RHEL, Fedora has inspired a variety of independent distributions. All-purpose distros, ones for live CDs, or for localizations, specific hardware or security and servers -- the Fedora derivatives include them all, creating an ecosystem of choices that sometimes resembles those available for Debian or Ubuntu, but also shows its own specializations.
Fedora uses the word "spin" for any result that contains only software from Fedora repositories, and "remix" for any result that contains software from other sources, distinguishing between the two by differences in trademarks. In addition, spins are registered and carried on many Fedora mirror sites as an official parts of Fedora.
The exact number of Fedora spin and remixes is hard to determine. With Fedora's Revisor tool, users can produce their own spins and remixes from the desktop. As a result, many spins and even more remixes are probably never registered. In fact, the ease of creating spins and remixes may explain why Fedora has fewer derivative distros than Debian -- for many purposes, producing a spin or remix is far easier than maintaining a distro.
Some of Fedora's spins provide a different desktop. Of these, the most popular is the KDE spin, since Fedora itself defaults to GNOME. In fact, the KDE spin is consistently the most popular one. However, those for Xfce and LXDE and Sugar on a Stick are among the most-often downloaded spins as well.
The line between derivatives and spins and remixes is especially thin among the all-purpose derivatives. For instance, aside from language, the point of Open Xange, a month-old Portuguese derivative, is largely that it uses KDE rather than GNOME. Similarly, Kororaa, which was originally a Gentoo derivative, is now dependent on Fedora. Kororaa's home page even goes so far as to describe the distro as a Fedora remix. Fusion would also count as a remix, since it contains non-free software that Fedora does not carry in its repositories.
A more ambitious general derivative is CentOS. Based largely on RHEL source code, CentOS is a community-based distribution for enterprise installations. Although lacking the resources that are behind RHEL and sometimes being slow to release, CentOS is probably the most-respected Fedora derivative. Given that CentOS provides still another level of testing and refinement, this reputation is understandable.
In its own way, Blag is no less ambitious. However, its goal is to make a distribution that only contains free software. Its name an acronym for Brixton Linux Action Group, the distribution reveals a fondness for activist rhetoric on its web site, and is one of a handful of distributions recognized by the Free Software Foundation as completely free. Blag recently released a new version based on Fedora 14, two and a half years after its last release.
Although Fedora and its spins are usually available as Live Media, derivatives designed specifically to be run as Live Media are relatively rare. A Japanese derivative called Berry appears to be the only one designed for general use as a demo.