The following is a brief overview of the various free BSD operating systems, their strengths and weaknesses, and their place in a market increasingly dominated by a few major Linux distributions.

History of BSD
Because of Unix's convoluted origins, no operating system today qualifies as "pure" Unix. The word "Unix" itself is trademarked by the Open Group, which inherited the mantle from AT&T, Unix's original developer. Today, the Open Group certifies various vendors as official distributors of Unix systems.

BSD, or the Berkeley Software Distribution, was created at the University of California at Berkeley and used AT&T code as its foundation. Many utilities that are now synonymous with Unix, such as the vi text editor, actually originated as part of BSD. Even more significantly, BSD included TCP/IP networking code in its kernel, directly enabling the rapid development of what we now know as the Internet.

Later, when licensing costs climbed and lawsuits threatened, BSD was stripped of all AT&T code. The last, completely AT&T-free version of BSD, 4.4BSD-Lite Release 2, was released in June 1995, and is the foundation for most of today's BSD-based operating systems. Hence, BSD systems can claim to be "Unix-like," but cannot bear the trademark "Unix." Similarly, Linux is another Unix clone, but derived from the Minix kernel.

Though freely distributed like Linux, the BSDs are licensed differently. The GNU General Public License, which governs the distribution of the Linux kernel, prevents developers from reusing code for commercial purposes without also redistributing any source code changes. This strategy encourages users to contribute back to the Linux community and hastens the pace of change (almost unbearably so), but discourages most serious commercial software development, since it's difficult to profit from intellectual property distributed as source code. While companies such as SGI and IBM have released portions of their intellectual property under the GPL (the XFS and JFS filesystems, respectively), we have yet to see a major application --- Photoshop or Microsoft Office, for instance -- incorporate GLD'ed code (legally, anyway).

The BSD license, however, permits unrestricted redistribution of code, even in binary form, so long as a copyright notice is attached. Consequently, the free BSDs each tend to have a smaller core group of developers and a unique focus. Also, most commercial operating systems owe a heavy debt to BSD, since BSD code can be used for commercial purposes without disclosure: BSD code is everywhere, even in Microsoft Windows, allegedly. (For on the history of BSD, click here.)

NetBSD
NetBSD's focus since its inception as the first spinoff of the original BSD project has been portability: it runs on over 50 architectures, including Sony's Playstation 2 and embedded systems. This makes it the most austere and least user-friendly of the free BSD distributions, but also the one that technical innovations tend to spring from. One of these is the binary emulation feature. Since all Unix and Unix-like systems have a similar set of system calls (open a file, close a file, etc.), it's possible to run a program compiled for one operating system under NetBSD by intercepting the system calls for the other OS and making the corresponding BSD system calls instead. This makes it ideal for users hoping to resuscitate old hardware, but who still need to run applications compiled for the old operating system. However, this is only true if the applications in question were compiled on the same architecture -- in other words, you can't install OpenBSD on a SGI machine and expect to run Microsoft Office, since Microsoft Office was originally compiled on a different type of processor.

FreeBSD
Far less portable than NetBSD, FreeBSD's developers emphasize enhancing the i386 and Alpha architectures, making it the most likely contender for Linux users who want to experiment with a new OS on their desktop. Version 5.0 of the operating system, though only released on Jan. 19 and not recommended for production purposes, includes Firewire and Bluetooth support and support for the UltraSPARC (64-bit) architecture.

FreeBSD suffers by comparison to Linux in its multiprocessor support, which, although improved in the 5.0 release, has been described by Jordan Hubbard, one of FreeBSD's founders, as "around 6 months" behind the Linux 2.4.x kernel. However, FreeBSD's software library is by far the largest of the BSDs: 8207 ported applications, at this writing, which puts it on a competitive stance even with the ubiquitous RedHat. In addition to this huge library, FreeBSD uses the Linux emulation layer from NetBSD, allowing it to run Linux binaries by intercepting the Linux system calls and making the appropriate BSD system calls instead. This emulation layer is extraordinarily effective, even permitting the execution of complex applications including Oracle and Mathematica -- although obtaining Oracle support for an emulated BSD installation is another matter.

OpenBSD
OpenBSD, a spinoff of the NetBSD project, has an almost immaculate security record, as advertised on its Web page: "Only one remote hole in the default install, in more than 7 years!" Each addition to the OpenBSD code undergoes extensive peer review and testing, resulting in perhaps the most secure Unix-like operating system on the planet (note that I said Unix-like; mainframes can sometimes boast of even greater security). Because of the emphasis on security, OpenBSD is not the premier choice for use as a desktop workstation, since most applications -- Web browsers, games, and the other things one might normally want to use a desktop computer for -- place little emphasis on security. OpenBSD is eminently suited for duty as a firewall or gateway server, though. OpenBSD's most famous offspring is OpenSSH, the open-source Secure Shell implementation.

Darwin
Though it's probably not a selling point for most Macintosh advocates, Macintosh OS X has a BSD-derived core known as Darwin. The BSD user community doesn't seem to have much enthusiasm for this development, judging from the dearth of news on the OpenDarwin page. This may be attributable to the Apple Public Source License that governs the Darwin code, which states that any source code improvements become Apple's property: yet another closed-source license at the open-source masquerade. Though Darwin's existence will no doubt assist the other BSDs in enhancing their PowerPC emulation, it seems unlikely to make other inroads.

Comparisons and Conclusions
Compared to Linux, the BSDs lack support from major vendors. While companies as diverse as SGI, IBM, and Sun have made major GPL'ed contributions to Linux, BSD developers have a rougher time of things. Sun, for instance, isn't disclosing secrets of the UltraSparc III architecture to the OpenBSD team, but provided access to Linux developers even before the processor's release.

The liberality of the BSD license itself is to blame. Releasing source code under the GPL is a winning proposition for corporations so inclined, because the license ensures that competitors won't benefit unduly from their work. Code released under the BSD license, however, is like grapes ripening on the vine. Sun released its OpenOffice suite under the Lesser GPL (LGPL), in the hopes that it would stem the Microsoft tide. Releasing it under the BSD license, however, would have provided any number of competitors with the foundation of a full-fledged office productivity suite, ready to be modified and resold. RedHat, similarly, spurns the BSD license in its own software, despite their willingness to profit from its fruits by repackaging BSD-licensed products such as PostgreSQL.

The freedom to profit that the BSD license protects is rarely acknowledged as being of equal necessity as the freedom of expression protected by the GPL -- after all, who's going to manufacture computers if they can't also sell software to run on them? However, the proportion of BSD-licensed code to GPL'ed code is undoubtedly decreasing. Lamentably, the increasing commercialization of academia makes it unlikely that the congruence of factors that led to the creation and widespread availability of the original BSD code will recur, and the Linux juggernaut may well be unstoppable at this late date. Despite this, the BSDs continue to be a source of original thinking and innovative design from which everyone benefits, however indirectly, and are well worth a look.

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