OpenBSD
OpenBSD is a free, open-source, and security-focused Unix-like operating system based on the Berkeley Software Distribution (BSD). It emphasizes correctness, security, and proactive auditing of its codebase, making it a popular choice for firewalls, routers, and other critical infrastructure. The project is known for its strict licensing, minimal default installation, and integrated security features like OpenSSH and LibreSSL.
Developers should learn OpenBSD when building secure network services, firewalls, or embedded systems where reliability and security are paramount, such as in financial or government applications. It's also valuable for those interested in operating system internals, as its clean code and documentation serve as an educational resource. Use cases include VPN gateways, DNS servers, and secure web servers due to its built-in tools and hardened defaults.