FreeBSD is one of a family of “BSD” operating system projects. “BSD” refers to the kind of license that all the source code is released under.

Related projects are NetBSD, OpenBSD, Darwin (used by Apple as part of MacOS 10), and the new DragonFly BSD project (which is an offshoot of FreeBSD 4.10). On a FreeBSD system, you can check the file /usr/share/misc/bsd-family-tree for more details. The latest version of that file can be seen at: http://www.FreeBSD.org/cgi/cvsweb.cgi/src/share/misc/bsd-family-tree

FreeBSD is used by some major network providers/ISPs (Yahoo, NTT/Verio, NY Internet)

Parts of FreeBSD are also picked up and used by some commercial OS's, such as MacOS 10, IRIX, Solaris. It is also used by some embedded systems.

The official “1.0 release” of FreeBSD was on November 1993

Official Release cycle:

Release 4 vs 5 vs 6 — Big Changes happen between these branches.

Release 4.8 vs 4.9 vs 4.10 — These are smaller, well-tested landmarks on the 4.x branch. API's and ABI's will usually be upwards compatible between these “minor” releases.

Release 5.2 vs 5.2.1 — Minor but significant fixes (to 5.2, in this example)

Meaning of the active “CVS branches” in the FreeBSD CVS repository

What CVS calls “MAIN” is what FreeBSD calls the CURRENT branch

CURRENT vs STABLE vs SECURITY and ERRATA

The RELENG_4 (4.x) branch was created in CVS around March 9, 2000 (which means “the 5.x-CURRENT series” started on that date).

On November 6, 2004, we made available 5.3-RELEASE, and that marks the official start of 5.x-STABLE series.

http://www.FreeBSD.org/releases/5.3R/announce.html – provides a short announcement for 5.3-RELEASE, information on various ways to obtain the release, and links to various pages that provide much more detail.