FreeBSD is an Open Source, standards-compliant, Unix-like operating system which began in 1993. FreeBSD is slightly more secure than Linux. One of the foundational pillars of the FreeBSD project was security. FreeBSD and other BSD-based systems share much in common with systems like Linux. FreeBSD has close roots to Unix systems of the past, while Linux was created from scratch as an open Unix-like alternative.
File systems supported by FreeBSD are UFS2, ZFS, ext2, ext3, FAT, ISO 9660, UDF and NFS. Computer architectures supported by FreeBSD are IA-32, x86-64, ARM, MIPS and PowerPC. The FreeBSD kernel type is Monolithic with modules.
BSD stands for "Berkeley Software Distribution". It is the name of distributions of source code from the University of California, Berkeley, which were originally extensions to AT&T’s Research UNIX operating system. Three popular derivatives known today are FreeBSD, OpenBSD, and NetBSD, which were born of 386BSD and 4.4BSD-Lite. Most of the current BSD operating systems are open source and available for download, free of charge, under the BSD License.
According to the FreeBSD Documentation Portal, FreeBSD aims for high performance and ease of use by end users, and is a favourite of web content providers. It runs on a number of platforms and has significantly more users than the other projects.
FreeBSD maintains a complete system, delivering a kernel, device drivers, userland utilities, and documentation, as opposed to Linux only delivering a kernel and drivers, and relying on third-parties like GNU for system software.
In January 1992, Berkeley Software Design Inc. (BSDi) started to release BSD/386, later called BSD/OS, an operating system similar to FreeBSD and based on 4.3BSD Net/2. AT&T filed a lawsuit against BSDi and alleged distribution of AT&T source code in violation of license agreements. The lawsuit was settled out of court. BSDi was forced to migrate their source base to the newer 4.4BSD-Lite2 sources. FreeBSD was also urged to move to 4.4BSD-Lite2. FreeBSD 2.0 which was released in 1994 is not supposed to contain any source code from AT&T. This purging of AT&T code places FreeBSD in the clear.
There are two known open source operating systems that mimic the look and feel of Mac OS that are developed from FreeBSD. The Operating Systems airyxOS and helloSystem copy the look and feel of OS X. Although they are not the only Mac OS X clones out there they are mentioned here because they are FreeBSD. Apple's Mac OS X is built from 4.4BSD-Lite2 and in a sense an early FreeBSD version. However, OS X is not FreeBSD and shares little with FreeBSD in its present state. OS X may still have FreeBSD's virtual file system, and network stack which will likely and inevitably be replaced at some point after this writing but this is not for certain. FreeBSD users will certainly feel comfortable at the Mac OS X CLI!