Several people and projects use CentOS or Red Hat Enterprise Linux as a base within which to build additional functionality. We note them alphabetically.
These products are NOT CentOS. This list is merely provided as a public service. Some may well be a downstream fork. ...
See also: CentOS news which contains far more products.
Amazon Linux AMI
The Amazon Linux AMI are Linux images provided by Amazon Web Services for use on their Amazon Elastic Compute Cloud (Amazon EC2) service. It's AMI product is a fork that varies from CentOS, that is maintained and supported by Amazon. Additionally third-parties publish pre-built images designed to run in Amazon's virtual machine infrastructure which may have started on a CentOS base. Such images usually (but not always) have modified kernels, or networking and storage access kernel modules, which not published by the CentOS project. Finally, CentOS' upstream has had a long term marketing relationship with Amazon.
AsteriskNOW is an open source Software Appliance based on CentOS. As it provides a modified kernel, please don't ask for help on CentOS channels but seek help from them. AsteriskNOW is currently at version 2.0.2 and is available in 32- and 64-bit-versions. Quoting from the webpage: "AsteriskNOW users have two options for support. There is an active community of AsteriskNOW users, integrators and developers who provide community support on the AsteriskNOW forums and mailing list."
BlueOnyx is a sub- or successor fork of BlueQuartz, it seems.
BlueQuartz was a community successor to the commercial Cobalt Qube and Raq distributions. The products were bought by Sun Microsystems and then abandoned in fairly short order. It appears to have been abandoned since 2007. (As to updates, early 2009.) Part of its updates were pulled from CentOS or upstream SRPMs.
CentServer takes CentOS-5 & RPMforge packages and then repacks / distributes (maintains?) their own version and repository. TruHuynh could not find the corresponding SRPMS at the time of this writing.
ClarkConnect is based on CentOS but uses their own repositories. (See, for instance, the CentOS RPMS in http://redhot.clarkconnect.com/community/5.0/System/RPMS/.)
ClearOS (formerly called ClarkConnect) is based on CentOS, according to http://www.clearfoundation.com/Software/distribution-timeline.html.
Elastix is based on CentOS-5 but requires the use of a deprecated CentOS-5.1 kernel (forum post), as of 2008/10/20. Update - as of 2010/10/10 they appear to be using a stealthily modified CentOS 5.5 kernel per this forum thread.
FAN's (Fully Automated Nagios') goal is to provide a CD based on CentOS.
OpenNode is another rebranded build ("OpenNode ISO installer will setup a minimal CentOS 5 server system . . .").
OpenVZ is container-based virtualization for Linux and the basis for Parallels Virtuozzo Containers (see below). It is a fork of CentOS which uses a number of non-standard packages (including the kernel) and is not supported by the CentOS community.
Oracle Unbreakable Linux
Oracle Unbreakable Linux is presently (2012) a rebuild of Red Hat Enterprise Linux, not CentOS. It is a commercial product with support provided by Oracle. There are some additional patches applied to the RHEL SRPMS.
OVH is providing a modified CentOS version with a modified kernel (126.96.36.199-grs (OVH)) and few others things. See the discussion on their forum (in French): http://forum.ovh.com/showthread.php?t=60009
Parallels Virtuozzo Containers
Parallels Virtuozzo Containers is an operating system virtualization solution. As with OpenVZ, it is not supported by the CentOS community.
PBX in a Flash is based on CentOS. It has its own custom installer and post-install scripts, along with its own update mechanism. From http://knol.google.com/k/ward-mundy/pbx-in-a-flash/3uqc77rg9tgar/2#: "If you update your CentOS configuration, you will need to reinstall it (PIAF) by running update-scripts, then update-fixes, and then install-netconfig." Hence, ask **them** if you break something.
R-fx add-on packages
R-fx adds packages which have been reported, on IRC, not to play well with the CentOS IPTables packet filtering and configuration tools.
trixbox (formerly Asterisk@Home)
trixbox is based on CentOS. See the trixbox FAQs: What about other hardware? How do I know if a particular NIC or motherboard is compatible?
The trixswitch ISO install package is a CentOS-based CD-ROM image that creates a boot CD which will automatically install a CentOS variant and FreeSWITCH.
VicidialNOW is a Linux Distribution, based on CentOS, that claims to provide a full 'Call Center Suite System'. It will automatically install Vicidial, Mysql, PHP, Asterisk, VtigerCRM and other open source components.
Whitebox Enterprise Linux
Whitebox Enterprise Linux was based on Red Hat Enterprise Linux. Its goal was to provide an unencumbered binary RPM based Linux distribution. Only EL3 and EL4 images were built during this project's life. It became unsupported when its maintainer was affected by the US Katrina Hurricane in 2005, the underlying distributions updates SRPMs went 'end of life', and is now largely of historical interest.
The text on this page is largely quoted from those projects, along with the links cited, and do not necessarily represent the opinions of CentOS.