What versions of BSD are available

In contrast to the numerous Linux distributions, there are only four major open source BSDs. Each BSD project maintains its own source tree and its own kernel. In practice, though, there appear to be fewer divergences between the userland code of the projects than there is in Linux.

It is difficult to categorize the goals of each project: the differences are very subjective. Basically,

• FreeBSD aims for high performance and ease of use by end users, and is a favourite of web content providers. It runs on a number of platforms, including i386™ based systems (“PCs”), systems based on the AMD 64-bit processors, UltraSPARC® based systems, systems based on Compaq's Alpha processors and systems based around the NEC PC-98 specification. The FreeBSD project has significantly more users than the other projects.
• NetBSD aims for maximum portability: “of course it runs NetBSD”. It runs on machines from palmtops to large servers, and has even been used on NASA space missions. It is a particularly good choice for running on old non-Intel® hardware.
• OpenBSD aims for security and code purity: it uses a combination of the open source concept and rigorous code reviews to create a system which is demonstrably correct, making it the choice of security-conscious organizations such as banks, stock exchanges and US Government departments. Like NetBSD, it runs on a number of platforms.
• DragonFlyBSD aims for high performance and scalability under everything from a single-node UP system to a massively clustered system. DragonFlyBSD has several long-range technical goals, but focus lies on providing a SMP-capable infrastructure that is easy to understand, maintain and develop for.