BSD (originally: Berkeley Software Distribution) refers to the particular version of the UNIX operating system that was developed at and distributed from the University of California at Berkeley. BSD UNIX has been popular and many commercial implementations of UNIX systems are based on or include some BSD code (Bron: whatis.com).
FreeBSD is an advanced operating system for x86 compatible, DEC Alpha, and PC-98 architectures. It is derived from BSD UNIX. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.
FreeBSD offers advanced networking, performance, security and compatibility features today which are still missing in other operating systems, even some of the best commercial ones.
FreeBSD makes an ideal Internet or Intranet server. It provides robust network services under the heaviest loads and uses memory efficiently to maintain good response times for thousands of simultaneous user processes.
The quality of FreeBSD combined with today’s low-cost, high-speed PC hardware makes FreeBSD a very economical alternative to commercial UNIX workstations. It is well-suited for a great number of both desktop and server applications.
While you might expect an operating system with these features to sell for a high price, FreeBSD is available free of charge and comes with full source code.