Linux
The Smoothwall Open Source Project was set up in 2000 to develop and maintain Smoothwall Express - a Free firewall that includes its own security-hardened GNU/Linux operating system and an easy-to-use web interface.
AV Linux is a free shared downloadable and installable snapshot ISO image based on Debian/GNU Linux pre-configured
Oracle Linux is an enterprise-class Linux distribution supported by Oracle and built from source packages for Red Hat Enterprise Linux (RHEL). Some of the special features of Oracle Linux include a custom-build and rigorously-tested Linux kernel called "Oracle Unbreakable Kernel"
Trisquel GNU/Linux is a distribution of the GNU operating system, with the Linux-libre kernel, derived from another distribution, Ubuntu. The project aims for a fully free software system without proprietary software or firmware and uses a version of Ubuntu's modified kernel
Clonezilla live is a partition and disk imaging/cloning program similar to True Image® or Norton Ghost®. It helps you to do system deployment, bare metal backup, and recovery.
DragonFly is an operating system and application environment designed as a continuation of the FreeBSD-4.x family. These operating systems and Linux can be classified as the same category because they are based on UNIX concepts and application programming interface.
NixOS is a GNU/Linux distribution that aims to improve the state of the art in system configuration management. In existing distributions, actions such as upgrades are dangerous: upgrading a package can cause other packages to break, upgrading an entire system is much less reliable