CentOS!

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. »

elementary OS is a free, fast and aesthetically pleasing operating system based on Ubuntu .

openSUSE is a free and Linux-based operating system for your PC, Laptop or Server.

Gentoo Linux is a versatile, fast, highly configurable and completely free Linux and FreeBSD distribution geared towards developers and network professionals.

Qubes is an open source operating system designed to provide strong security for desktop computing.

Red Hat is the leader in development, deployment, and management of Linux and open source solutions for Internet infrastructure - ranging from embedded devices to secure Web servers. Red Hat was founded in 1994 by visionary entrepreneurs Bob Young and Marc Ewing. Open source is the foundation of our business model. It represents a fundamental shift in how software is created. The code that makes up the software is available to anyone. Developers who use the software are free to improve the software. The result: rapid innovation. Red Hat solutions combine Red Hat Linux, developer and embedded technologies, training, management services, technical support. We deliver this open source innovation to our customers via an Internet platform called Red Hat Network. Red Hat is headquartered in Raleigh, North Carolina, USA. »

The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. Our efforts emphasize portability, standardization, correctness, proactive security and integrated cryptography.

SliTaz GNU/Linux LiveCD operating system. "SliTaz is a free operating system, working completely in RAM and booting from removable media such as a cdrom or USB key. SliTaz is distributed as a LiveCD, and weighs less than 30MB. The system is quick and responsive, clean and robust. SliTaz is simple and intuitive, providing a lightweight, elegant desktop, detailed documentation and easy to use configuration tools."

KDE neon is a Kubuntu-based Linux distribution and live DVD featuring the latest KDE Plasma desktop and other KDE community software. Besides the installable DVD image, the project provides a rapidly-evolving software repository with all the latest KDE software. Two editions of the product are available - a "User" edition, designed for those interested in checking out the latest KDE software as it gets released, and a "Developer's" edition, created as a platform for testing cutting-edge KDE applications. »