https://en.wikipedia.org/wiki/Berkeley_Software_Distribution
Derived from AT&T.
OS X is a fork.
Major differences from Linux:
- license: BSD license, which allowed Apple to fork
- scope: the project also includes userspace utilities. Interesting as it ensures that they work together with the kernel.
Why it lost from Linux: http://serverfault.com/questions/36359/why-is-linux-more-popular-than-bsd An important factor was the AT&T legal case against BSD at the kernel explosion of the early 90's, which held it back at the critical moment. GPL also likely helped Linux by forcing enterprises to contribute and not only leech.
Main variants:
- FreeBSD
- OpenBSD
- NetBSD
Major users: https://www.freebsdfoundation.org/testimonials include:
- Netflix
- Xinuous
- Experts Exchange