FreeBSD is a Unix-like operating system descended from Unix via the BSD branch through 386BSD and 4.4BSD. It runs on processors compatible with the Intel x86 family, as well as on the DEC Alpha, the UltraSPARC processors by Sun Microsystems, the Itanium (IA-64) and AMD64 processors. Support for the PowerPC architecture is in development. It is generally regarded as being quite reliable and robust.
Initial development of FreeBSD was started in November of 1993 by Jordan Hubbard, and took its sources from 386BSD. However, due to concerns about the legality of all the sources used in 386BSD, FreeBSD re-engineered much of the system with the FreeBSD 2.0 release in January of 1995 using the 4.4BSD-Lite release from the University of California, Berkeley, and again at FreeBSD 3.0 using the 4.4BSD-Lite2 release.
The current (January 2004) FreeBSD release is FreeBSD 5.2. FreeBSD developers maintain (at least) two branches of simultaneous development: a -STABLE version of FreeBSD, which produces releases about once every 4-6 months. The latest STABLE release of FreeBSD is 4.9. The other development branch, -CURRENT, contains aggressive new kernel and userspace features. At the time of writing, the 5.x release series is cut from the 5-CURRENT branch, but has already produced 5.2-RELEASE. The FreeBSD development team has announced that the 5-CURRENT branch will become 5-STABLE around 5.3-RELEASE, at which point a 6-CURRENT branch will be created.
FreeBSD is released under the BSD License, which allows everyone to use and redistribute FreeBSD as they wish, as long as they do not remove the copyright notice and the BSD license itself (which does not prohibit re-licensing).
FreeBSD 5 includes a number of new features, including many that are security related. The TrustedBSD project was formed for the express purpose of adding trusted operating system functionality to the FreeBSD operating system. An extensible Mandatory Access Control framework (the TrustedBSD MAC Framework), filesystem Access Control Lists (ACLs) and the new UFS2 filesystem all came from TrustedBSD. Some of the TrustedBSD functionality has been integrated into the NetBSD and OpenBSD operating systems as well.
A derivative version based on the GNU toolset is currently being developed by Debian as Debian GNU/FreeBSD. An innovative new FreeBSD 4.x variant called DragonFlyBSD is in the works which will at some point feature a message-passing system similar to that found in microkernels.