Free and open-source software (FOSS) is software that is distributed in a manner that allows its users to run the software for any purpose, to redistribute copies of it, and to examine, study, and modify, the source code. FOSS is also a loosely associated movement of multiple organizations, foundations, communities and individuals who share basic philosophical perspectives and collaborate practically, but might diverge in detail questions.

The historical precursor to this was the hobbyist and academic public domain software ecosystem of the 1960s to 1980s. The FOSS movement's "free" part originates from Richard Matthew Stallman, who noted the lost freedom to users on the decline of the public domain ecosystem and the growth of a copyrighted proprietary software ecosystem. In response, as a hack of the copyright system, he created the GPL, a protective copyleft license, aiming for the creation of a complete and free operating system — GNU. Shortly after, the BSDs (FreeBSD, OpenBSD, NetBSD) brought an alternative FOSS approach to the table: the more public domain–like permissive licenses. Other noteworthy FOSS organizations from this time include the Apache Foundation (Apache Server), GNOME, Debian, Mozilla Foundation (Firefox), with their own ideas: The Free Software Definition, Debian Free Software Guidelines, The Open Source Definition, and more. At the end of the 1990s, in the context of the dot-com bubble and web 2.0, the Open-Source movement (with Eric S. Raymond, Bruce Perens, Tim O'Reilly and others) gave important impulses to FOSS with the achieved open sourcing of Netscape's browser as Firefox and Sun Microsystems' office suite, OpenOffice.org. The incorporation of Linus Torvalds' Linux kernel in FOSS OS paved the way to broad mainstream recognition and acceptance of FOSS in the IT domain and among the general public. In the 2010s GitHub's openness and collaboration encouraging software repository cloud service brought FOSS software development & maintenance methodologies to mainstream software development.The FOSS movement inspired the creation of other movements, such as open access, open hardware, open content, free culture, open standards, and many more.

Adblock Plus (ABP) is a free and open-source browser extension for content-filtering and ad blocking. It is developed by Eyeo GmbH, a German software company. The extension has been released for Mozilla Firefox (including mobile), Google Chrome, Internet Explorer, Microsoft Edge (Chromium based version), Opera, Safari, Yandex Browser, and Android.

In 2011, Adblock Plus and Eyeo attracted considerable controversy over its "Acceptable Ads" program to "allow certain non-intrusive ads" (such as Google Ads) to be allowed under the extension's default settings. While participation in the whitelisting process was free for small websites, large advertising companies were required to pay a fee in order for their ads to be whitelisted. (Full article...)

Although there was free software before, in 1983 Richard Stallman launched the free software movement and founded the Free Software Foundation to promote the movement and to publish its own definition of free software. Others have published alternative definitions of free software, including the Debian Free Software Guidelines and the Berkeley Software Distribution-based operating system communities.

In 1998, Bruce Perens and Eric S. Raymond began a campaign to market open-source software and founded the Open Source Initiative, which espoused different goals and a different philosophy from Stallman's.

The following operating systems are released under free software licenses:

Impediments and challenges

Digital Millennium Copyright Act · Digital rights management · Tivoization · Software patents and free software · Trusted Computing · Proprietary software · SCO-Linux controversies · Binary blobs

Adoption issues

OpenDocument format · Vendor lock-in · GLX · Free standards · Free software adoption cases

About licences

Free software licences · Copyleft · List of FSF-approved software licenses

Common licences

GNU General Public License · GNU Lesser General Public License · GNU Affero General Public License · IBM Public License · Mozilla Public License · Permissive free software licences

History

...of free software · Free software movement · Timeline of free and open-source software

Groupings of software

Comparison of free software for audio · List of open-source video games

Naming issues

GNU/Linux naming controversy · Alternative terms for free software · Naming conflict between Debian and Mozilla

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The following Wikimedia Foundation sister projects provide more on this subject:

• Project selected articles archive
• Wikipedia free and open-source software task force