FreeBSD has similarities with Linux, with two major differences in scope and license: FreeBSD maintains a complete operating system, ie the project provides the kernel, device drivers, user space, and documentation, unlike Linux which provides only the kernel and drivers and leaves the system software to third parties. FreeBSD source code is usually released under a permissive BSD license as opposed to the Linux GPL copyleft.
The FreeBSD project includes a security team supervising all software integrated in the base distribution. A small range of third-party applications can be installed using the package management system of the FreeBSD Ports, or by directly compiling the source code. Due to its terms of permissive license, much of the FreeBSD code has become an integral part of other operating systems such as Juniper JUNOS and OS X from Apple.