From a system administrator's point of view, FreeBSD is closer to a specific Linux distribution than to Linux in general. The BSD projects each maintain and distribute a set of core software including a kernel, some basic system and networking utilities, a command line interface. Additionally the base system contains some third-party software that is closely integrated with the base system such as Perl.
The difference with a Linux distribution is that Linux distribution maintainers are mostly distinct from Linux utility maintainers. The core system utilities in a Linux distributions come from many sources (kernel, init, GNU or BusyBox core utilities, bash, etc.) whereas BSD distributions each have their own set.
If you want to know what's in the base FreeBSD packages, the best way is to install it (possibly in a VM). Everything in
/usr is the “base system”; additional third-party software (packages and ports, in BSD terminology) lives in
/usr/local. If you don't want to install, you can download the installation archives (
base.txz for FreeBSD, e.g. 9.1 i386
base.txz) and look at their content. Alternatively, you can browse the source.