The current (February 2004) FreeBSD release is FreeBSD 5.2.1.
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 4.10. 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
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. FreeBSD 5 also has support for encrypted filesystems, through the GDBE system written by Poul-Henning Kamp. 
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-distribution under another license).
DragonFly BSD is a fork from FreeBSD 4.8 that is intended to be the logical continuation of the FreeBSD 4 series. It will feature a threaded message passing system similar to that found in microkernels.