FreeBSD is a 4.4BSD-Lite based operating system for Intel (x86 and Itanium), AMD64, ARM, and Sun UltraSPARC computers. Ports to other architectures are also under way. You can also read about the history of FreeBSD, or the current release. If you are interested in contributing something to the Project (code, hardware, funding), see the Contributing to FreeBSD article.
FreeBSD has many noteworthy features. Some of these are:
Multi-user facilities which allow many people to use a FreeBSD system simultaneously for a variety of things. This means, for example, that system peripherals such as printers and tape drives are properly shared between all users on the system or the network and that individual resource limits can be placed on users or groups of users, protecting critical system resources from over-use.
Strong TCP/IP networking with support for industry standards such as SCTP, DHCP, NFS, NIS, PPP, SLIP, IPsec, and IPv6. This means that your FreeBSD machine can interoperate easily with other systems as well as act as an enterprise server, providing vital functions such as NFS (remote file access) and email services or putting your organization on the Internet with WWW, FTP, routing and firewall (security) services.
Thousands of ready-to-run applications are available from the FreeBSD ports and packages collection. Why search the net when you can find it all right here?
Thousands of additional and easy-to-port applications are available on the Internet. FreeBSD is source code compatible with most popular commercial UNIX systems and thus most applications require few, if any, changes to compile.
Source code for the entire system means you have the greatest degree of control over your environment. Why be locked into a proprietary solution at the mercy of your vendor when you can have a truly open system?
Extensive online documentation.
And many more!
FreeBSD is based on the 4.4BSD-Lite release from Computer Systems Research Group (CSRG) at the University of California at Berkeley, and carries on the distinguished tradition of BSD systems development. In addition to the fine work provided by CSRG, the FreeBSDProject has put in many thousands of hours in fine tuning the system for maximum performance and reliability in real-life load situations. FreeBSD offers performance and reliability on par with commercial offerings, combined with many cutting-edge features not available anywhere else.
The applications to which FreeBSD can be put are truly limited only by your own imagination. From software development to factory automation, inventory control to azimuth correction of remote satellite antennae; if it can be done with a commercial UNIX product then it is more than likely that you can do it with FreeBSD too! FreeBSD also benefits significantly from literally thousands of high quality applications developed by research centers and universities around the world, often available at little to no cost. Commercial applications are also available and appearing in greater numbers every day.
Because the source code for FreeBSD itself is generally available, the system can also be customized to an almost unheard of degree for special applications or projects, and in ways not generally possible with operating systems from most major commercial vendors. Here is just a sampling of some of the applications in which people are currently using FreeBSD:
Internet Services: The robust TCP/IP networking built into FreeBSD makes it an ideal platform for a variety of Internet services such as:
Education: Are you a student of computer science or a related engineering field? There is no better way of learning about operating systems, computer architecture and networking than the hands on, under the hood experience that FreeBSD can provide. A number of freely available CAD, mathematical and graphic design packages also make it highly useful to those whose primary interest in a computer is to get other work done!
Research: With source code for the entire system available, FreeBSD is an excellent platform for research in operating systems as well as other branches of computer science. FreeBSD's freely available nature also makes it possible for remote groups to collaborate on ideas or shared development without having to worry about special licensing agreements or limitations on what may be discussed in open forums.
Networking: Need a new router? A name server (DNS)? A firewall to keep people out of your internal network? FreeBSD can easily turn that unused PC sitting in the corner into an advanced router with sophisticated packet-filtering capabilities.
Embedded: FreeBSD makes an excellent platform to build embedded systems upon. With support for the ARM, MIPS and PowerPC platforms, coupled with a robust network stack, cutting edge features and the permissive BSD license FreeBSD makes an excellent foundation for building embedded routers, firewalls, and other devices.
Desktop: FreeBSD makes a fine choice for an inexpensive desktop solution using the freely available X11 server. FreeBSD offers a choice from many open-source desktop environments, including the standard GNOME and KDE graphical user interfaces. FreeBSD can even boot “diskless” from a central server, making individual workstations even cheaper and easier to administer.
Software Development: The basic FreeBSD system comes with a full complement of development tools including a full C/C++ compiler and debugger suite. Support for many other languages are also available through the ports and packages collection.
FreeBSD is available to download free of charge, or can be obtained on either CD-ROM or DVD. Please see AppendixA, Obtaining FreeBSD for more information about obtaining FreeBSD.
FreeBSD's advanced features, proven security, predictable release cycle, and permissive license have led to its use as a platform for building many commercial and open source appliances, devices, and products. Many of the world's largest IT companies use FreeBSD:
Apache - The Apache Software Foundation runs most of its public facing infrastructure, including possibly one of the largest SVN repositories in the world with over 1.4 million commits, on FreeBSD.
Apple - OS X borrows heavily from FreeBSD for the network stack, virtual file system, and many userland components. Apple iOS also contains elements borrowed from FreeBSD.
Cisco - IronPort network security and anti-spam appliances run a modified FreeBSD kernel.
Citrix - The NetScaler line of security appliances provide layer 4-7 load balancing, content caching, application firewall, secure VPN, and mobile cloud network access, along with the power of a FreeBSD shell.
Dell KACE - The KACE system management appliances run FreeBSD because of its reliability, scalability, and the community that supports its continued development.
Experts Exchange - All public facing web servers are powered by FreeBSD and they make extensive use of jails to isolate development and testing environments without the overhead of virtualization.
Isilon - Isilon's enterprise storage appliances are based on FreeBSD. The extremely liberal FreeBSD license allowed Isilon to integrate their intellectual property throughout the kernel and focus on building their product instead of an operating system.
iXsystems - The TrueNAS line of unified storage appliances is based on FreeBSD. In addition to their commercial products, iXsystems also manages development of the open source projects TrueOS and FreeNAS.
Juniper - The JunOS operating system that powers all Juniper networking gear (including routers, switches, security, and networking appliances) is based on FreeBSD. Juniper is one of many vendors that showcases the symbiotic relationship between the project and vendors of commercial products. Improvements generated at Juniper are upstreamed into FreeBSD to reduce the complexity of integrating new features from FreeBSD back into JunOS in the future.
McAfee - SecurOS, the basis of McAfee enterprise firewall products including Sidewinder is based on FreeBSD.
NetApp - The Data ONTAP GX line of storage appliances are based on FreeBSD. In addition, NetApp has contributed back many features, including the new BSD licensed hypervisor, bhyve.
Netflix - The OpenConnect appliance that Netflix uses to stream movies to its customers is based on FreeBSD. Netflix has made extensive contributions to the codebase and works to maintain a zero delta from mainline FreeBSD. Netflix OpenConnect appliances are responsible for delivering more than 32% of all Internet traffic in North America.
Sandvine - Sandvine uses FreeBSD as the basis of their high performance real-time network processing platforms that make up their intelligent network policy control products.
Sony - The PlayStation 4 gaming console runs a modified version of FreeBSD.
Sophos - The Sophos Email Appliance product is based on a hardened FreeBSD and scans inbound mail for spam and viruses, while also monitoring outbound mail for malware as well as the accidental loss of sensitive information.
Spectra Logic - The nTier line of archive grade storage appliances run FreeBSD and OpenZFS.
Stormshield - Stormshield Network Security appliances are based on a hardened version of FreeBSD. The BSD license allows them to integrate their own intellectual property with the system while returning a great deal of interesting development to the community.
The Weather Channel - The IntelliStar appliance that is installed at each local cable provider's headend and is responsible for injecting local weather forecasts into the cable TV network's programming runs FreeBSD.
Verisign - Verisign is responsible for operating the .com and .net root domain registries as well as the accompanying DNS infrastructure. They rely on a number of different network operating systems including FreeBSD to ensure there is no common point of failure in their infrastructure.
Voxer - Voxer powers their mobile voice messaging platform with ZFS on FreeBSD. Voxer switched from a Solaris derivative to FreeBSD because of its superior documentation, larger and more active community, and more developer friendly environment. In addition to critical features like ZFS and DTrace, FreeBSD also offers TRIM support for ZFS.
WhatsApp - When WhatsApp needed a platform that would be able to handle more than 1 million concurrent TCP connections per server, they chose FreeBSD. They then proceeded to scale past 2.5 million connections per server.
Wheel Systems - The FUDO security appliance allows enterprises to monitor, control, record, and audit contractors and administrators who work on their systems. Based on all of the best security features of FreeBSD including ZFS, GELI, Capsicum, HAST, and auditdistd.
FreeBSD has also spawned a number of related open source projects:
BSD Router - A FreeBSD based replacement for large enterprise routers designed to run on standard PC hardware.
FreeNAS - A customized FreeBSD designed to be used as a network file server appliance. Provides a python based web interface to simplify the management of both the UFS and ZFS file systems. Includes support for NFS, SMB/CIFS, AFP, FTP, and iSCSI. Includes an extensible plugin system based on FreeBSD jails.
GhostBSD - A desktop oriented distribution of FreeBSD bundled with the Gnome desktop environment.
mfsBSD - A toolkit for building a FreeBSD system image that runs entirely from memory.
NAS4Free - A file server distribution based on FreeBSD with a PHP powered web interface.
OPNSense - OPNsense is an open source, easy-to-use and easy-to-build FreeBSD based firewall and routing platform. OPNsense includes most of the features available in expensive commercial firewalls, and more in many cases. It brings the rich feature set of commercial offerings with the benefits of open and verifiable sources.
TrueOS - A customized version of FreeBSD geared towards desktop users with graphical utilities to exposing the power of FreeBSD to all users. Designed to ease the transition of Windows and OS X users.
pfSense - A firewall distribution based on FreeBSD with a huge array of features and extensive IPv6 support.
ZRouter - An open source alternative firmware for embedded devices based on FreeBSD. Designed to replace the proprietary firmware on off-the-shelf routers.
FreeBSD is also used to power some of the biggest sites on the Internet, including:
and many more. Wikipedia also maintains a list of products based on FreeBSD.