Security-focused operating system

This is a list of operating systems specifically focused on security. Similar concepts include security-evaluated operating systems that have achieved certification from an auditing organization, and trusted operating systems that provide sufficient support for multilevel security and evidence of correctness to meet a particular set of requirements.

Android-based

 * CalyxOS is designed for privacy, security, and accessibility.
 * DivestOS is a fork of LineageOS that aims to increase privacy and security.
 * GrapheneOS is a privacy and security-focused mobile operating system for selected Google Pixel smartphones and tablets.
 * Kali NetHunter is a mobile penetration testing platform based on Kali Linux.

Arch-based

 * BlackArch is a penetration testing distribution that provides a large number of security tools.

Debian-based

 * Kali Linux is designed for digital forensics and penetration testing.
 * Parrot OS Security Edition is designed for penetration testing, vulnerability assessment and mitigation, computer forensics, and anonymous web browsing.
 * Tails is aimed at preserving privacy and anonymity.
 * Whonix consists of two virtual machines. All communications are forced through Tor.

Gentoo-based

 * Pentoo is a Live CD and Live USB designed for penetration testing and security assessment.

Other Linux distributions

 * Alpine Linux is designed to be small, simple, and secure. It uses musl, BusyBox, and OpenRC instead of the more commonly used glibc, GNU Core Utilities, and systemd.
 * Fedora Silverblue is an immutable desktop operating system. Every Silverblue installation is identical to every other installation of the same version, and it never changes as it is used.

BSD

 * OpenBSD is a Unix-like operating system that emphasizes portability, standardization, correctness, proactive security, and integrated cryptography.

Xen

 * Qubes OS aims to provide security through isolation. Isolation is provided through the use of virtualization technology. This allows the segmentation of applications into secure virtual machines.