Free and open-source software

A screenshot of free and open-source software (FOSS): Linux Mint running the Xfce desktop environment, Firefox, a calculator program, the built-in calendar, Vim, GIMP, and VLC media player

Software that is both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source code is openly shared so that people are encouraged to voluntarily improve the design of the software.

- Free and open-source software

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Android (operating system)

Mobile operating system based on a modified version of the Linux kernel and other open source software, designed primarily for touchscreen mobile devices such as smartphones and tablets.

Android 12 home screen with Pixel Launcher
Android 12 home screen with Pixel Launcher
HTC Dream or T-Mobile G1, the first commercially released device running Android (2008)
Eric Schmidt, Andy Rubin and Hugo Barra at a 2012 press conference announcing Google's Nexus 7 tablet
Frontal buttons (home, menu/options, go back, search) and optical track pad of an HTC Desire, a 2010 smartphone with Android OS.
The stack of Android Open Source Project
Android's architecture diagram
The first-generation Nexus 7 tablet, running Android 4.1 Jelly Bean
Barnes & Noble Nook running Android
Ouya, a video game console which runs Android
Android-x86 running on an ASUS Eee PC netbook

The core components are taken from the Android Open Source Project (AOSP), which is free and open-source software (FOSS) primarily licensed under the Apache License.

Open-source software

Part of the broader term free and open-source software.

A screenshot of Manjaro running the Cinnamon desktop environment, Firefox accessing Wikipedia which uses MediaWiki, LibreOffice Writer, Vim, GNOME Calculator, VLC and Nemo file manager, all of which are open-source software.
The logo of the Open Source Initiative

However, while Free and open-source software has historically played a role outside of the mainstream of private software development, companies as large as Microsoft have begun to develop official open-source presences on the Internet.

Linux kernel

Linux kernel 3.0.0 booting
Linux kernel 3.0.0 booting
Linus Torvalds at the LinuxCon Europe 2014 in Düsseldorf
The Linux kernel supports various hardware architectures, providing a common platform for software, including proprietary software.
Map of the Linux kernel
Four interfaces are distinguished: two internal to the kernel, and two between the kernel and userspace.
At XDC2014, Alex Deucher from AMD announced the unified kernel-mode driver. The proprietary Linux graphic driver, libGL-fglrx-glx, will share the same DRM infrastructure with Mesa 3D. As there is no stable in-kernel ABI, AMD had to constantly adapt the former binary blob used by Catalyst.
The Linux Storage Stack Diagram
TiVo DVR, a consumer device running Linux
An example of Linux kernel panic
An iPod booting iPodLinux
Redevelopment costs of Linux kernel
Boot messages of a Linux kernel 2.6.25.17

The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel.

Free-software license

Notice that grants the recipient of a piece of software extensive rights to modify and redistribute that software.

The free-software-licensing spectrum and some examples of programs under those licenses
License compatibility between common FOSS software licenses according to David A. Wheeler (2007): the vector arrows denote a one directional compatibility, therefore better compatibility on the left side ("permissive licenses") than on the right side ("copyleft licenses")

Software using such a license is free software (or free and open-source software) as conferred by the copyright holder.

FreeBSD

FreeBSD 13.0 bootloader with ASCII art logo
FreeBSD 13.0 bootloader with ASCII art logo
FreeBSD 13.0 startup with console login prompt
PC-BSD version 10, the operating system that was later known as TrueOS

FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix.

NetBSD

NetBSD 9.2 showing XDM
NetBSD 9.2 showing XDM
NetBSD/amd64 startup in console mode
NetBSD/amd64 console login and welcome message
NetBSD was used in NASA's SAMS-II Project of measuring the microgravity environment on the International Space Station, and for investigations of TCP for use in satellite networks.

NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD).

Free software movement

Social movement with the goal of obtaining and guaranteeing certain freedoms for software users, namely the freedoms to run the software, to study the software, to modify the software, and to share copies of the software .

Richard Stallman circa 2002, founder of the GNU Project and the free software movement.
GNU and Tux mascots around free software supporters at FISL 16

Like many social movements, the free software movement has ongoing internal conflict between the many FLOSS organizations (FSF, OSI, Debian, Mozilla Foundation, Apache Foundation, etc.) and their personalities.

OpenBSD

OpenBSD 7.0 default desktop with various utilities: top, xterm, xcalc, and glxgears
OpenBSD 7.0 default desktop with various utilities: top, xterm, xcalc, and glxgears
Bar chart showing the proportion of users of each BSD variant from a 2005 BSD usage survey of 4330 users.
OpenBSD console login and its messages
OpenBSD developers at c2k1 hackathon at MIT, June 2001
OpenBSD hackathon s2k17

OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD).

Fork (software development)

In software engineering, a project fork happens when developers take a copy of source code from one software package and start independent development on it, creating a distinct and separate piece of software.

A timeline chart of how Linux distributions have forked

Free and open-source software is that which, by definition, may be forked from the original development team without prior permission, and without violating copyright law.

Firefox

Firefox 100 on Windows 11
Firefox 100 on Windows 11
Screenshot of Phoenix 0.1 on Windows XP
The result of the Acid3 test on Firefox 17
Firefox 57 on macOS High Sierra
Firefox 96 on Arch Linux
Logo used for Iceweasel
Firefox mascot at the FISL16 (2015), Brazil
Usage share of web browsers according to StatCounter.
Logo of "Phoenix" and "Firebird" before being renamed as Firefox
Firefox 0.8–0.10, from February 9, 2004 to November 8, 2004
Firefox 1.0–3.0, from November 9, 2004 to June 29, 2009
Firefox 3.5–22, from
Firefox 23–56, from August 6, 2013 to November 13, 2017<ref>{{cite web|last=Martell|first=Sean|title=(Re)building a simplified Firefox logo|url=http://blog.seanmartell.com/2013/06/27/rebuilding-a-simplified-firefox-logo/|work=Reticulating Splines|access-date=September 5, 2013|date=June 27, 2013|archive-url=https://web.archive.org/web/20130702182008/http://blog.seanmartell.com/2013/06/27/rebuilding-a-simplified-firefox-logo/|archive-date=July 2, 2013|url-status=live}}</ref>
Firefox 57–69, from November 14, 2017 to October 21, 2019
The 2011 Nightly logo, used to represent nightly builds of pre-alpha versions
The 2013 Nightly logo
The 2017 Nightly logo
The 2019 Nightly logo
The 2011 Aurora logo, used to represent an alpha release
The 2013 Aurora logo
The 2015 Developer Edition logo
The 2017 Developer Edition logo
The 2019 Developer Edition logo
Blue globe artwork, distributed with the source code, and is explicitly not protected as a trademark<ref>Mozilla Trademark Policy FAQ {{Webarchive|url=https://web.archive.org/web/20130407213521/http://www.mozilla.org/foundation/trademarks/faq.html|date=April 7, 2013 }}: "What are the Mozilla Trademarks and Logos?". Retrieved November 2, 2006</ref>
The logo for the Firefox brand of products and services, as of July 2019. It appears as if the fox was removed, but this is not the logo for the browser itself.

Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation.