Although Windows and Linux dominate most headlines about server operating systems, many system administrators prefer the stability and security of BSD (Berkeley Software Distribution). BSD is a Unix-like operating system, originally developed at the University of California at Berkeley. Although the original code is scarcely used anymore, it has many descendants, including the following:
FreeBSD – This is the most popular of the descendants and has its own variations, including DragonFly BSD and PC-BSD, which is primarily a desktop distribution. Apple’s Darwin, which is the core of Mac OS X, is also a derivative of FreeBSD.
NetBSD – This variation is primarily built for portability, stability, and clean design.
OpenBSD – It originally began as a fork of NetBSD and as developed in a very security-conscious operating systems. The creators of the OS are also responsible for OpenSSH, OpenBGPD, OpenNTPD, and OpenSSL OpenCVS, projects with security in mind.
While there are many other descendants of BSD, these are the most popular ones, with FreeBSD and OpenBSD being the primary dedicated server versions used around the world. BSD users pride themselves on the stability of their operating systems, evident in their extremely long uptimes (sometimes over a year or longer).
As to whether their assertions hold any validity, I will leave it for you to decide for yourself. Like Linux, these BSD variants are all free and open source operating systems that anyone can download and install. They are released under a unique set of licenses that are variations of the original BSD license, a more permissive license than the GNU GPL.