Here's a list of some Linux Desktop Operating System distributions:

Source is Distrowatch

Ubuntu is a complete desktop Linux operating system, freely available with both community and professional support. The Ubuntu community is built on the ideas enshrined in the Ubuntu Manifesto: that software should be available free of charge, that software tools should be usable by people in their local language and despite any disabilities, and that people should have the freedom to customise and alter their software in whatever way they see fit. "Ubuntu" is an ancient African word, meaning "humanity to others". The Ubuntu distribution brings the spirit of Ubuntu to the software world.

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The Fedora Project is an openly-developed project designed by Red Hat, open for general participation, led by a meritocracy, following a set of project objectives. The goal of The Fedora Project is to work with the Linux community to build a complete, general purpose operating system exclusively from open source software. Development will be done in a public forum. The project will produce time-based releases of Fedora about 2-3 times a year, with a public release schedule. The Red Hat engineering team will continue to participate in building Fedora and will invite and encourage more outside participation than in past releases. By using this more open process, we hope to provide an operating system more in line with the ideals of free software and more appealing to the open source community.

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Linux Mint is an Ubuntu-based distribution whose goal is to provide a more complete out-of-the-box experience by including browser plugins, media codecs, support for DVD playback, Java and other components. It also adds a custom desktop and menus, several unique configuration tools, and a web-based package installation interface. Linux Mint is compatible with Ubuntu software repositories.

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The openSUSE project is a community program sponsored by Novell. Promoting the use of Linux everywhere, this program provides free, easy access to openSUSE, a complete Linux distribution. The openSUSE project has three main goals: make openSUSE the easiest Linux for anyone to obtain and the most widely used Linux distribution; leverage open source collaboration to make openSUSE the world's most usable Linux distribution and desktop environment for new and experienced Linux users; dramatically simplify and open the development and packaging processes to make openSUSE the platform of choice for Linux developers and software vendors.

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PCLinuxOS is a user-friendly Linux distribution with out-of-the-box support for many popular graphics and sound cards, as well as other peripheral devices. The bootable live CD provides an easy-to-use graphical installer and the distribution sports a wide range of popular applications for the typical desktop user, including browser plugins and full multimedia playback. The intuitive system configuration tools include Synaptic for package management, Addlocale to add support to many languages, Getopenoffice to install the latest OpenOffice.org, and Mylivecd to create a customised live CD.

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The Debian Project is an association of individuals who have made common cause to create a free operating system. This operating system is called Debian GNU/Linux, or simply Debian for short. Debian systems currently use the Linux kernel. Linux is a completely free piece of software started by Linus Torvalds and supported by thousands of programmers worldwide. Of course, the thing that people want is application software: programs to help them get what they want to do done, from editing documents to running a business to playing games to writing more software. Debian comes with over 20,000 packages (precompiled software that is bundled up in a nice format for easy installation on your machine) - all of it free. It's a bit like a tower. At the base is the kernel. On top of that are all the basic tools. Next is all the software that you run on the computer. At the top of the tower is Debian -- carefully organizing and fitting everything so it all works together.

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Mandriva Linux was launched in 1998 under the name of Mandrake Linux, with the goal of making Linux easier to use for everyone. At that time, Linux was already well-known as a powerful and stable operating system that demanded strong technical knowledge and extensive use of the command line; MandrakeSoft saw this as an opportunity to integrate the best graphical desktop environments and contribute its own graphical configuration utilities to quickly become famous for setting the standard in Linux ease of use. In February 2005, MandrakeSoft merged with Brazil's Conectiva to form Mandriva S.A., with headquarters in Paris, France. The company's flagship product, Mandriva Linux, offers all the power and stability of Linux to both individuals and professional users in an easy-to-use and pleasant environment.

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Sabayon Linux is a live DVD designed to transform a computer into a powerful Gentoo Linux system in less than 5 minutes. Gentoo Linux is a Linux distribution powered by a software install manager engine called "Portage". Besides functioning as a live DVD, Sabayon Linux can also be installed on a hard disk, acting effectively as an easy-to-use Gentoo installation disk. The live DVD includes a large range of desktop environments and open source software applications, such as KDE, GNOME, XFce, Fluxbox, KOffice, OpenOffice.org, FreeNX, amaroK, Kaffeine, etc.

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Arch Linux is an independently developed, i686- and x86_64-optimised Linux distribution targeted at competent Linux users. It uses 'pacman', its home-grown package manager, to provide updates to the latest software applications with full dependency tracking. Operating on a rolling release system, Arch can be installed from a CD image or via an FTP server. The default install provides a solid base that enables users to create a custom installation. In addition, the Arch Build System (ABS) provides a way to easily build new packages, modify the configuration of stock packages, and share these packages with other users via the Arch Linux user repository.

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MEPIS Linux is a Debian-based desktop Linux distribution designed for both personal and business purposes. It includes cutting-edge features such as a live, installation and recovery CD, automatic hardware configuration, NTFS partition resizing, ACPI power management, WiFi support, anti-aliased TrueType fonts, a personal firewall, KDE, and much more.

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Puppy Linux is yet another Linux distribution. What's different here is that Puppy is extraordinarily small, yet quite full featured. Puppy boots into a 64MB ramdisk, and that's it, the whole caboodle runs in RAM. Unlike live CD distributions that have to keep pulling stuff off the CD, Puppy in its entirety loads into RAM. This means that all applications start in the blink of an eye and respond to user input instantly. Puppy Linux has the ability to boot off a flash card or any USB memory device, CDROM, Zip disk or LS/120/240 Superdisk, floppy disks, internal hard drive. It can even use a multisession formatted CD-R/DVD-R to save everything back to the CD/DVD with no hard drive required at all!

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The Official Release of Slackware Linux by Patrick Volkerding is an advanced Linux operating system, designed with the twin goals of ease of use and stability as top priorities. Including the latest popular software while retaining a sense of tradition, providing simplicity and ease of use alongside flexibility and power, Slackware brings the best of all worlds to the table. Originally developed by Linus Torvalds in 1991, the UNIX-like Linux operating system now benefits from the contributions of millions of users and developers around the world. Slackware Linux provides new and experienced users alike with a fully-featured system, equipped to serve in any capacity from desktop workstation to machine-room server. Web, ftp, and email servers are ready to go out of the box, as are a wide selection of popular desktop environments. A full range of development tools, editors, and current libraries is included for users who wish to develop or compile additional software.

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Ultimate Edition, first released in December 2006, is a fork of Ubuntu. The goal of the project is to create a complete, seamlessly integrated, visually stimulating, and easy-to-install operating system. Single-button upgrade is one of several special characteristics of this distribution. Other main features include custom desktop and theme with 3D effects, support for a wide range of networking options, including WiFi and Bluetooth, and integration of many extra applications and package repositories.

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FreeBSD is a UN*X-like operating system for the i386, IA-64, PC-98, Alpha/AXP, and UltraSPARC platforms based on U.C. Berkeley's "4.4BSD-Lite" release, with some "4.4BSD-Lite2" enhancements. It is also based indirectly on William Jolitz's port of U.C. Berkeley's "Net/2" to the i386, known as "386BSD", though very little of the 386BSD code remains. FreeBSD is used by companies, Internet Service Providers, researchers, computer professionals, students and home users all over the world in their work, education and recreation.

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CentOS as a group is a community of open source contributors and users. Typical CentOS users are organisations and individuals that do not need strong commercial support in order to achieve successful operation. CentOS is 100% compatible rebuild of the Red Hat Enterprise Linux, in full compliance with Red Hat's redistribution requirements. CentOS is for people who need an enterprise class operating system stability without the cost of certification and support.

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Tiny Core Linux is a very small (10 MB) minimal Linux desktop. It is based on Linux 2.6 kernel, BusyBox, Tiny X, FLTK graphical user interface and flwm window manager, running entirely in memory. It is not a complete desktop, nor is all hardware completely supported; it represents only the core needed to boot into a very minimal X Window desktop, typically with wired Internet access. This minimal desktop can be extended by installing additional applications from online repositories.

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From the website:

Kongoni is the Shona word for a Gnu (also known as a Wildebeest) the animal which inspired the name of the GNU operating system. The name represents the spirit and history of Kongoni, a GNU/Linux operating system of African origin.

Kongoni is a desktop oriented operating system with a strong belief in being truly free software. This means that Kongoni will neither include nor ship any software not under a license approved by the free software foundation.

The system is meant to be easy to install, use and customize. Kongoni targets 32 and 64 bit Intel compatible chipsets with native versions for each.
The core OS is shipped as a runnable and installable live CD. Each version is compatible with the slackware release it is based on and can natively install packages for slackware (32-bit) and bluewhite64 (64-bit) respectively.

Our own shipped packages use a powerful mechanism for installation knowns as ports. Ports mean that the programs are downloaded as source and packages are then built automatically (no user knowledge required). This means smaller bandwidth requirements (a big concern in Africa) and programs that run faster and use less memory.

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Security Focused Distributions:

ClearOS is a network and gateway server designed for small businesses and distributed environments. Based on CentOS, a clone of Red Hat Enterprise Linux, the distribution includes an extensive list of features and integrated services which are easy to configure through an intuitive web-based interface. Some of the tools found in ClearOS include antivirus, antispam, VPN, content filtering, bandwidth manager, SSL certification, and web log analyser, just to name a few of the available modules. The distribution is provided as a free download, inclusive of free security updates for 18 months.

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BackTrack is an Ubuntu-based distribution with a collection of security and forensics tools. It was created by merging Auditor Security Linux with WHAX (formerly Whoppix).

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eBox Platform is a unified network server that offers easy and efficient computer network administration for small and medium-size businesses. It can act as a gateway, an infrastructure manager, a unified threat manager, an office server, a unified communication server or a combination of them. These functionalities are tightly integrated, automating most tasks, avoiding mistakes and saving time for system administrators. eBox Platform is released under the GNU General Public License (GPL) and runs on top of Ubuntu.

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Untangle Gateway is a Debian-based network gateway with pluggable modules for network applications like spam blocking, web filtering, anti-virus, anti-spyware, intrusion prevention, VPN, SSL VPN, firewall, and more.

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FreeNAS is an embedded open source NAS (Network-Attached Storage) distribution based on FreeBSD, supporting the following protocols: CIFS (samba), FTP, NFS, TFTP, AFP, RSYNC, Unison, iSCSI (initiator and target) and UPnP.

It supports Software RAID (0,1,5), ZFS, disk encryption, S.M.A.R.T/email monitoring with a WEB configuration interface (from m0n0wall).

FreeNAS can be installed on Compact Flash/USB key, hard drive or booted from LiveCD.

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NexentaStor is an enterprise-class unified storage solution built upon the foundation of the open-source file system Nexenta Core Platform, including the ZFS file system. NexentaStor adds to the open source foundation a complete set of managed features, including ZFS and synchronous block level replication, integrated search, console and graphical user interfaces, and optional advanced features, such as management of storage for leading virtualised environments, enhanced mapping and management for Fiber Channel and iSCSI environments, and active/active high availability. A free "developer's edition" based on the most recent stable Nexenta Core Platform is available free of charge for users with less than 4 terabyte of used disk space.

Clonezilla Live is a Debian-based live CD containing Clonezilla, a partition and disk cloning software similar to Norton Ghost. It saves and restores only used blocks in hard drive. With Clonezilla, one can clone a 5 GB system to 40 clients in about 10 minutes.

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System Rescue CD is a Gentoo-based Linux system on a bootable CD-ROM or USB drive, designed for repairing a system and data after a crash. It also aims to provide an easy way to carry out administration tasks on a computer, such as creating and editing hard disk partitions. It contains many useful system utilities (GNU Parted, PartImage, FSTools) and some basic ones (editors, Midnight Commander, network tools). It aims to be very easy to use. The kernel of the system supports all of today's most important file systems, including ext2, ext3, ext4, ReiserFS, Reiser4FS, btrfs, XFS, JFS, VFAT, NTFS, ISO9660, as well as network file systems, such as Samba and NFS.

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Parted Magic is a small live CD/USB/PXE with its elemental purpose being to partition hard drives. Although GParted and Parted are the main programs, the CD/USB also offers other applications, such as Partition Image, TestDisk, fdisk, sfdisk, dd, ddrescue, etc.

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Astaro offers an integrated software solution that provides superior performance in an all-in-one firewall. Its hardened operating system, stateful packet inspection, content filtering (virus & surf protection), application proxies and IPsec based VPN provides a powerful solution to today's security issues. It is designed to maximize your networks security without compromising its performance enabling telecommuters, branch offices, customers and suppliers to safely share critical business information. Our proprietary user interface, WebAdmin allows ease of use and manageability of all open source firewall components, as well as the Up2Date service via the Internet. It is easy to install with all components on one CD achieving simple implementation and integration to existing network environments.

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Webconverger is a live, Debian-based web kiosk. It is designed for deployments in places like offices or Internet cafés where only web applications are used. The web site argues that the software is ideal because of the following reasons:

• No users - no superuser
• Stability & security of open source - based on GNU/Linux Debian stable releases
• No local user data - Locked down browser kiosk - for example no functionality to save bookmarks locally
• Zero maintenance - Automatic upgrades -- this has not been achieved yet
• Less is more - Minimal packages for just the Web experience (though that includes Adobe flash and pdf support)
• Excellent i18n support
• Committed to user's privacy
• (Long term) Universal commitment to all devices - Webconverger focuses on 486 builds which should run on any PC, new or old.

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IPFire is a Linux distribution that focusses on easy setup, good handling and high level of security. It is operated via an intuitive web-based interface which offers many configuration options for beginning and experienced system administrators. IPFire is maintained by developers who are concerned about security and who update the product regularly to keep it secure. IPFire ships with a custom package manager called Pakfire and the system can be expanded with various add-ons.

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SME Server (known as e-smith at the time) was founded in January 1999 by Joseph and Kim Morrison. The company introduced the first version of its flagship software product, the e-smith server and gateway, in April 1999. By the end of the year, many thousands of e-smith servers were running in countries from Fiji to Finland. Word was spreading quickly among developers and systems integrators who needed a solid, easy-to-use server for their small-business customers. In July 2001, e-smith was acquired by Mitel Networks, in September 2004 by Lycoris, and the project is currently sponsored by Resource Strategies, Inc.

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IPCop Linux is a complete Linux Distribution whose sole purpose is to protect the networks it is installed on. After seeing the direction certain Linux Distributions were heading in, a group of dissatisfied users/developers decided that there was little reason for the idea of a GPL Linux Firewall Distribution of such potential to be, simply, extinguished. By implementing existing technology, outstanding new technology and secure programming practices IPCop is the Linux Distribution for those wanting to keep their computers/networks safe. The IPCop Linux Team is dedicated to doing the very best job possible to keep your systems safe, as you can see on our site. "The Bad Packets Stop Here!"

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Linux for Education:

Qimo 4 Kids is a distribution of Linux, derived from the popular Ubuntu, customised for use by children ages 3 and up. It comes pre-installed with free and open source games that are both educational and entertaining, with many more educational titles available for download from Ubuntu. The interface of Qimo 4 Kids has been specifically designed to be easy to navigate by the youngest of users.

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openSUSE-Edu Li-f-e (Linux for Education)

openSUSE Education team is proud to present openSUSE-Edu Li-f-e(Linux for Education) based on openSUSE 11.2. We are for the first time using "hybrid" iso image, single iso can be used to create live DVD or USB stick.

The iso image is created using the same KIWI imaging technology that is used to create official openSUSE medias.

This release includes carefully selected softwares for students, educators as well as parents. The software selection encompasses everything required to make computers productive for either home or educational use.

The Live DVD contains KIWI-LTSP server that can be enabled even by non-technical user, with tons of applications from openSUSE Education repository. With the KIWI-LTSP server you can PXE(network) boot other PCs to use this live DVD without installing or modifying anything on them. Booting from hard disk again will leave those PCs as they were.(Please note that running LTSP from Live DVD/USB is meant for demo/testing purpose only, install on the hard disk to use it in production).

This distribution includes LAMP (LAMP stands for Linux, Apache, MySQL and PHP) that is needed for developing or hosting PHP websites and all other major development tools. An award-winning Sugar desktop for children is also included in this media.

The aim of this DVD is to provide complete education and development resources for parents, students, teachers as well as IT admins running labs at educational institutes, if you think there is something missing that you absolutely must have on the DVD, drop us a line in Education/Talk:Live or on the bugzilla.

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Edubuntu is a partner project of Ubuntu Linux, a distribution suitable for classroom use. The aim is that an educator with limited technical knowledge and skill will be able to set up a computer lab, or establish an on-line learning environment, in an hour or less, and then administer that environment without having to become a fully-fledged Linux geek.

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Debian Edu / Skolelinux

• Debian Edu   is a Debian project to make the best distribution for educational purposes.
   You can read more about here.   

  Skolelinux   is the name of a Debian Pure Blend which is produced by the Debian Edu project.
   "Skole" ([skuːl]) is the Norwegian form of "school". Both "skole" and "school" comes from the Latin word "schola".

Goals

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  • tailored for the needs and use-cases in educational scenarios.  
  • preconfigured for easy installation (standalone, as well as network-wide rollout).  
  • easy to use, maintain, and administer.  

  • supporting your language natively.  

• Classify and package all free software related to education.  
• Write documentation to describe how to use the various softwares (in an educational context).  
• International availability, currently being translated into XX languages
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• Knosciences is a bootable CD with a collection of GNU/Linux software, automatic hardware [detection, and support for many graphics cards, sound cards, SCSI and USB devices and other peripherals.

  It is not necessary to install anything on a hard disk. Due to on-the-fly decompression, the CD can have up to 2 GB of executable software installed on it.