FreeBSD

A high-performance Unix-like operating system built for stability, advanced networking, and massive storage scalability.

FreeBSD delivers a complete operating system derived from Berkeley Software Distribution (BSD) heritage. It powers heavy-duty infrastructure like Netflix (Open Connect CDN) and WhatsApp (massive-scale messaging) using its legendary network stack and ZFS storage. The system maintains a unified source tree: the core team manages the base system while the Ports Collection (30,000+ packages) handles third-party software. It scales efficiently (supporting 128+ cores) and offers robust security features like Capsicum (sandboxing) and Jails (lightweight virtualization).

https://www.freebsd.org