Security-focused operating system

This is a list of operating systems specifically focused on security. Operating systems for general-purpose usage may be secure without having a specific focus 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 in general is very secure, having many security features such as taking advantage of SELinux and Verified Boot. CalyxOS is a free and open source privacy and security focused Android custom ROM DivestOS is a free and open source privacy and security focused Android custom ROM GrapheneOS is a free and open source privacy and security focused Android custom ROM Kali NetHunter is a free and open source privacy and security focused Android custom ROM for penetration testing Subgraph is a Linux-based operating system designed to be resistant to surveillance and interference by sophisticated adversaries over the Internet. Subgraph OS is designed with features that aim to reduce the attack surface of the operating system, and increase the difficulty required to carry out certain classes of attack. This is accomplished through system hardening and a proactive, ongoing focus on security and attack resistance. Subgraph OS also places emphasis on ensuring the integrity of installed software packages through deterministic compilation. Subgraph OS features a kernel hardened with the Grsecurity and PaX patchset, Linux namespaces, and Xpra for application containment, mandatory file system encryption using LUKS, resistance to cold boot attacks, and is configured by default to isolate network communications for installed applications to independent circuits on the Tor anonymity network. Tails is a security-focused Linux distribution aimed at preserving privacy and anonymity. It is meant to be run as Live-CD or from a USB Drive and to not write any kind of data to a drive, unless specified or persistence is set.