Linux
From The Psych Ward wiki
Linux (Linux Is Not UNIX) is a POSIX-compliant operating system, despite the name, many Linux "distros" are UNIX certified[1][2], or are UNIX compliant (such as RHEL and Slackware[citation needed]). The Psych Ward runs on a VPS (Virtual Private Server) running AlmaLinux 9.7, an RHEL compatible distribution. Multiple of TPW members also use Linux, notably Sara, Nětka, and Sans.
Linux is mainly used by Paraphiles due to its improved privacy compared to Windows or macOS. However its security is considered subpar compared to macOS, mainly for the reason that it does not have any exploit protection.