I wouldn’t refer to FreeBSD being the antithesis of Linux, since we both have similarities and are both Unix-like. But the similarities do lend people to think that FreeBSD is a Linux Distribution. However, that is not the case. FreeBSD is descended from the Unix developed at the University of California, Berkeley in the 1970s. Linux, on the other hand, was built as an open source alternative to UNIX. The similarities do make it easier for Linux developers to get involved with FreeBSD.

Currently there are over 400 active developers and thousands of contributors. FreeBSD works on 32- and 64-bit Intel / AMD x86, 32- and 64-bit Arm, RISC-V, PowerPC, Sparc64, and MIPS CPUs, and cloud providers like AWS, Azure, and GCP. There are tens of millions of deployed systems.

As with other BSDs, the FreeBSD base system is an integrated operating system distribution that is developed and released as a cohesive whole by a single team, which is in contrast to the Linux approach of distributions picking up the kernel from one source, the C library from another, the userland tools from another and so on.

FreeBSD operates on the Principle of Least Astonishment. In other words, don’t break things that work. Because the OS doesn’t change without good reason, if you are basing your code or product on it, you don't have to constantly catch up everytime there is a new OS release. It also makes upgrading relatively painless. The licensing model is probably the biggest difference between the two. Linux is under the GNU General Public License (GPL), meaning in part, that any derivative work of a product released under the GPL must also be supplied with source code if requested. FreeBSD on the other hand, is under the copy-free BSD license. It’s less restrictive: binary-only distributions are allowed and particularly useful for embedded platforms.