FreeBSD

TrustedBSDFreeBSD kernel*BSDFreeBSD ProjectLinux emulationSysinstallFAMPsFree BSDFreeBSD 12.0FreeBSD 4
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix.wikipedia
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FreeBSD Ports

FreeBSD Ports collectionportsports tree
A wide range of additional third-party applications may be installed using the pkg package management system or FreeBSD Ports, or by compiling source code.
The FreeBSD Ports collection is a package management system for the FreeBSD operating system, providing an easy and consistent way of installing software packages.

FreeNAS

Due to its licensing, much of FreeBSD's codebase has become an integral part of other operating systems, such as Apple's Darwin (the basis for macOS, iOS, watchOS, and tvOS), FreeNAS (an open-source NAS/SAN operating system), and the system software for Sony's PlayStation 3 and PlayStation 4.
FreeNAS is a free and open-source network-attached storage (NAS) software based on FreeBSD and the OpenZFS file system.

Linux

GNU/LinuxLinux on the desktopLin
FreeBSD has similarities with Linux, with two major differences in scope and licensing: FreeBSD maintains a complete system, i.e. the project delivers a kernel, device drivers, userland utilities, and documentation, as opposed to Linux only delivering a kernel and drivers, and relying on third-parties for system software; and FreeBSD source code is generally released under a permissive BSD license, as opposed to the copyleft GPL used by Linux.
Although not released until 1992, due to legal complications, development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux.

Darwin (operating system)

DarwinDarwin operating systemOpenDarwin
Due to its licensing, much of FreeBSD's codebase has become an integral part of other operating systems, such as Apple's Darwin (the basis for macOS, iOS, watchOS, and tvOS), FreeNAS (an open-source NAS/SAN operating system), and the system software for Sony's PlayStation 3 and PlayStation 4.
The kernel of Darwin is XNU, a hybrid kernel which uses OSFMK 7.3 (Open Software Foundation Mach Kernel) from the OSF, various elements of FreeBSD (including the process model, network stack, and virtual file system), and an object-oriented device driver API called I/O Kit.

Network-attached storage

NASnetwork attached storageStorage
Due to its licensing, much of FreeBSD's codebase has become an integral part of other operating systems, such as Apple's Darwin (the basis for macOS, iOS, watchOS, and tvOS), FreeNAS (an open-source NAS/SAN operating system), and the system software for Sony's PlayStation 3 and PlayStation 4.
For example, FreeNAS or NAS4Free, both open source NAS solutions designed for commodity PC hardware, are implemented as a stripped-down version of FreeBSD.

IXsystems

The company later renamed itself to The FreeBSD Mall and later iXsystems.
Its principal products are customized open source FreeBSD distributions, including the desktop operating system TrueOS (formerly PC-BSD) and the file servers and network attached storage systems FreeNAS and TrueNAS.

Free and open-source software

free and open-sourcefree and open source softwareFOSS
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix.
FreeBSD and NetBSD (both derived from 386BSD) were released as Free software when the USL v. BSDi lawsuit was settled out of court in 1993.

Unix-like

*nixUnixlike
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix.
These patterns do not literally match many system names, but are still generally recognized to refer to any UNIX system, descendant, or work-alike, even those with completely dissimilar names such as Darwin/macOS, illumos/Solaris or FreeBSD.

Operating system

operating systemsOScomputer operating system
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix.
NEXTSTEP would later be acquired by Apple Inc. and used, along with code from FreeBSD as the core of Mac OS X (macOS after latest name change).

Kernel (operating system)

kerneloperating system kernelkernels
FreeBSD has similarities with Linux, with two major differences in scope and licensing: FreeBSD maintains a complete system, i.e. the project delivers a kernel, device drivers, userland utilities, and documentation, as opposed to Linux only delivering a kernel and drivers, and relying on third-parties for system software; and FreeBSD source code is generally released under a permissive BSD license, as opposed to the copyleft GPL used by Linux.
Modern monolithic kernels, such as those of Linux and FreeBSD, both of which fall into the category of Unix-like operating systems, feature the ability to load modules at runtime, thereby allowing easy extension of the kernel's capabilities as required, while helping to minimize the amount of code running in kernel space.

Keith Bostic

After releasing Net-1, Keith Bostic, a developer of BSD, suggested replacing all AT&T code with freely-redistributable code under the original BSD license.
Among many other tasks, he led the effort at CSRG to create a free software version of BSD UNIX, which helped allow the creation of FreeBSD, NetBSD and OpenBSD.

GEOM

GEOM is a modular framework that provides RAID (levels 0, 1, 3 currently), full disk encryption, journaling, concatenation, caching, and access to network-backed storage.
GEOM is the main storage framework for the FreeBSD operating system.

Robert Watson (computer scientist)

Robert WatsonRobert N. M. Watson
The project was founded by Robert Watson with the goal of implementing concepts from the Common Criteria for Information Technology Security Evaluation and the Orange Book.
Robert Nicholas Maxwell Watson (born 3 May 1977) is a FreeBSD developer, and founder of the TrustedBSD Project.

Jordan Hubbard

Jordan K. Hubbard
In addition to that, the company employed Jordan Hubbard and David Greenman, ran FreeBSD on its servers, sponsored FreeBSD conferences and published FreeBSD-related books, including The Complete FreeBSD by Greg Lehey.
Jordan K. Hubbard (born April 8, 1963) is an open source software developer, authoring software such as the Ardent Window Manager and various other open source tools and libraries before co-founding the FreeBSD project with Nate Williams and Rodney W. Grimes in 1993, for which he contributed the initial FreeBSD Ports collection, package management system and sysinstall.

Poul-Henning Kamp

GBDE was written by Poul-Henning Kamp and is distributed under the two-clause BSD license.
Poul-Henning Kamp has been committing to the FreeBSD project for most of its duration.

OpenBSD

PuffyOpenCVSPuffy (mascot)
As of FreeBSD 5.4, support for the Common Address Redundancy Protocol (CARP) was imported from the OpenBSD project.
In September 2005, the BSD Certification Group surveyed BSD users, showing that 33 percent used OpenBSD, behind FreeBSD with 77 percent and ahead of NetBSD with 16 percent.

Ipfirewall

ipfwIPFW2Dummynet
FreeBSD ships with three different firewall packages: IPFW, pf and IPFilter.
ipfirewall or ipfw is a FreeBSD IP, stateful firewall, packet filter and traffic accounting facility.

GBDE

FreeBSD provides two frameworks for data encryption: GBDE and Geli.
GBDE, standing for GEOM Based Disk Encryption, is a block device-layer disk encryption system written for FreeBSD, initially introduced in version 5.0.

BSD licenses

BSD licenseBSDNew BSD License
FreeBSD has similarities with Linux, with two major differences in scope and licensing: FreeBSD maintains a complete system, i.e. the project delivers a kernel, device drivers, userland utilities, and documentation, as opposed to Linux only delivering a kernel and drivers, and relying on third-parties for system software; and FreeBSD source code is generally released under a permissive BSD license, as opposed to the copyleft GPL used by Linux. After releasing Net-1, Keith Bostic, a developer of BSD, suggested replacing all AT&T code with freely-redistributable code under the original BSD license.
An even more simplified version has come into use, primarily known for its usage in FreeBSD.

Geli (software)

GELI
FreeBSD provides two frameworks for data encryption: GBDE and Geli.
geli is a block device-layer disk encryption system written for FreeBSD, introduced in version 6.0.

ZFS

ZFS on LinuxMacZFSFUSE port for Linux
From 7.0 onward, FreeBSD supports the ZFS filesystem.
ZFS also includes a mechanism for dataset and pool level snapshots and replication, including snapshot cloning which is described by the FreeBSD documentation as one of its "most powerful features", having features that "even other file systems with snapshot functionality lack".

PlayStation 4

PS4PlayStation 4 Pro4
Due to its licensing, much of FreeBSD's codebase has become an integral part of other operating systems, such as Apple's Darwin (the basis for macOS, iOS, watchOS, and tvOS), FreeNAS (an open-source NAS/SAN operating system), and the system software for Sony's PlayStation 3 and PlayStation 4.
The PlayStation 4's operating system is called "Orbis OS", based upon a customized FreeBSD 9.

OpenZFS

feature flags
However, the FreeBSD project is still developing and improving its ZFS implementation via the OpenZFS project.
OpenZFS brings together developers from the illumos, Linux, FreeBSD, and macOS platforms, and a wide range of companies.

OpenPAM

DARPA/SPAWAR contract N66001-01-C-8035
For example, OpenPAM has been adopted by NetBSD.
OpenPAM is a BSD-licensed implementation of PAM used by FreeBSD, NetBSD, DragonFly BSD and macOS (starting with Snow Leopard),

Computer Systems Research Group

CSRGCSRG, UC BerkeleyU.C. Berkeley
Supported by funding from DARPA, the Computer Systems Research Group started to modify and improve AT&T Research Unix.
The group was disbanded in 1995, leaving a significant legacy: FreeBSD, OpenBSD, NetBSD, and DragonFly BSD are based on the 4.4BSD-Lite distribution and continue to play an important role in the open-source UNIX community today, including dictating the style of C programming used via KNF in the style man page.