FreeBSD is a free, open source, community operating system based on BSD UNIX. The project saw the light of day in 1993.
FreeBSD emphasises performance and functionalities. It incorporates advanced storage (ZFS), network, and security (i.e. Mac and BSM audit framework) functionalities. It is primarily used on the web and at the core of proprietary hardware (Juniper and NetApp, etc.).
FreeBSD is distributed under the BSD License.
The majority of its code is written in C.