The BSDs in general have fragmented rather less than GNU/Linux development has, though the latter have also captured a far larger deployment base, by most estimates. Adding Android to the mix, Linux competes with any end-user platform. BSD is also the root of many proprietary Unix variants, an intentional characteristic of its licensing model.
FreeBSD in general is aimed at the server and desktop niche with a particular expertise in networking. FreeBSD originated in the "UNIX Wars" of the early 1990s during which AT&T attempted to assert its trademark and copyright over the increasingly popular BSD and 386BSD ("1-800-ITS-UNIX") operating systems. That case was a landmark, with AT&T substantially failing to assert its claims. The ruling was largely sealed, but much of it was subsequently unsealed during the SCO v. IBM trial, greatly damaging SCO's case (also based on copyright claims over UNIX). Arguably the uncertainty generated by the lawsuit provided a toehold for Linux to gain in early critical popularity, though the openness of its development model also likely contributed to this.
NetBSD forked from FreeBSD with the aim of providing as broad a range of hardware support as possible, though arguably some GNU/Linux distros such as Debian have trumped it.
OpenBSD forked from NetBSD with the aim of providing a very high security platform. OpenBSD lags in many high-performance and scalability characteristics, but offers an exceptionally robust security profile and default deployment security characteristics. The project website has long bragged about its security record (presently "Only two remote holes in the default install, in a heck of a long time!"). Notable OpenBSD projects include the pf firewall suite and OpenSSH. There's also been a project to remove all GPL'd code from the OpenBSD release, though attempts by the original pf author to write a specific exclusion into his license for use in GPLd projects (which the BSD license otherwise allows) resulted in that codebase being removed and the suite rewritten from the ground up. Theo's ideological purity is different from Stallman's in bent, but no less strong in my opinion.
There are a few even smaller distros (notably DragonflyBSD), I'm less familiar with these.
Underlying all of the BSDs is the BSD license, which is "permissive", requiring only that the license text be included in derivative works -- those works themselves need not carry source distribution obligations as most of the GNU licenses (GPL, LGPL, GPLV2, GPLV3) do. The result (intentional) is that the BSDs are used in a wide range of proprietary products, not merely dedicated servers. I've found BSD in routers, load balancers, printers, fax machines, settops, and other devices, usually identifiable by nmap fingerprinting scans.