OpenBSD

Webiste: https://www.openbsd.org/

OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD. According to the website, the OpenBSD project emphasizes "portability, standardization, correctness, proactive security and integrated cryptography."

The OpenBSD project maintains portable versions of many subsystems as packages for other operating systems. Because of the project's emphasis on code quality, many components are reused in other software projects. Android's Bionic C standard library is based on OpenBSD code, LLVM uses OpenBSD's regular expression library, and Windows 10 uses OpenSSH (OpenBSD Secure Shell) with LibreSSL.