Open-source software

Lore & Background

Open-source software has its roots in the culture of source code sharing that dates back to the origins of computing in the 1950s. Major examples include the Linux kernel and the Firefox web browser. MediaWiki, the software powering Wikipedia, is itself an example of open-source software. The Open Source Definition (OSD) was based on the Debian Free Software Guidelines, written and adapted primarily by Bruce Perens and Eric S. Raymond. The OSI maintains a list of approved licenses that conform to the OSD. However, the OSI holds no legal authority over the term 'open source' and its definition is a matter of social convention. With its non-discrimination criteria having generated for decades what is described as a 'culture war' within software communities over the very meaning of open source — the OSI can be seen by some actors as an oppressive dogma. These disputes are driven by ethical and commercial concerns. Diverging visions and semantic conflicts around the meaning of open source have led to the creation of adjacent terms, such as source-available software, fair source, ethical source, shared source, post open source or fauxpen source. Public-domain software is a source of disagreement as to whether it qualifies as open source software, carrying no formal licence and granting rights that vary significantly depending on the jurisdiction.

Reader's Guide

Open-source software has become the backbone of the global digital infrastructure, powering domains such as web servers, cloud computing, supercomputers, mobile devices, artificial intelligence, and Internet of Things. A 2022 estimate suggests that between 80 and 96 percent of the code making up software on the market today, including proprietary software, is of open-source origin. Its adoption has grown steadily across public institutions, the private sector, and academia, driven by motivations of cybersecurity, digital sovereignty, and independence from proprietary software, with significant geopolitical implications. Organizations are increasingly setting up Open Source Program Offices to manage their strategies. Open-source software offers a range of benefits, but also presents specific risks and challenges. It can provide improved accessibility through lower and shared costs, greater adaptability through customization, transparency with auditable code, better interoperability via open standards, and independence from vendor lock-in, among others. Due to its ubiquity in modern software, open-source software raises major cybersecurity concerns, as well as significant maintenance challenges. The term 'open source' can be used in ways that do not conform to the OSD, ranging from unintentional misuse to deliberate rejection of its authority. Free and open-source software (FOSS) or free/libre and open-source software (FLOSS) is openly shared source code that is licensed without any restrictions on usage, modification, or distribution. Confusion persists about this definition because the 'free', also known as 'libre', refers to the freedom of the product, not the price. Richard Stallman of the FSF flatly opposes the term 'Open Source' being applied to what they refer to as 'free software', considering equating the terms incorrect and misleading.

Did You Know?

• A 2022 estimate suggests that between 80 and 96 percent of code in software on the market is of open-source origin.
• The Open Source Definition was based on the Debian Free Software Guidelines, written primarily by Bruce Perens and Eric S. Raymond.
• MediaWiki, the software powering Wikipedia, is itself an example of open-source software.

The Spectrum Between Proprietary and Open

Source-available software occupies a middle ground in the software distribution landscape. In its broadest interpretation, any program that ships with its source code qualifies, regardless of what legal permissions the user actually holds to use, modify, share, or even compile that code. This means a title like id Software's Doom can simultaneously be source-available and proprietary. The narrower interpretation, however, deliberately excludes software that meets the criteria for free or open-source designation. The official definitions from the Open Source Initiative and the Free Software Foundation demand substantially more: users must be granted rights to employ the software in derived commercial products, typically with attribution. So while every FOSS license is technically a source-available license under the broad reading, the term in its narrow sense is reserved specifically for offerings that fall short of those additional guarantees. The licenses in this space span a wide range, from mere permission to inspect code for reference purposes all the way to allowing modification and redistribution for both commercial and non-commercial ends.

Anti-Competitive Clauses and the Vendor Lock-In Effect

A particularly contentious subset of source-available licensing involves what are termed noncompete licenses. These are essentially closed-source licenses constructed by taking an existing open-source license and grafting onto it a clause that forbids the user from deploying the software in a manner that competes with the original developer. The practical effect is a form of vendor lock-in: users who wish to exploit the software commercially are steered toward negotiating a separate, often paid, agreement directly with the developer. This architecture deliberately channels economic value back to the licensor while still offering the appearance of transparency through code disclosure. The result is a hybrid model where the source is visible but the freedom to act on that visibility is curtailed in ways that the Open Source Initiative and the Free Software Foundation do not recognize as acceptable. These arrangements sit in a gray zone, offering more than pure proprietary software yet falling well short of the freedoms that define the open-source movement.

A Catalog of Restrictive License Instruments

The landscape of non-free source-available licenses is remarkably diverse. Fossa, Inc. Sentry followed in November 2023 with the Functional Source License, a simpler alternative that restricts competing use for a limited period before the code transitions to Apache or MIT licensing. MongoDB's Server Side Public License modifies the AGPL so that incorporating the software into a user-facing service obligates releasing the entire service's source, a condition the OSI, Debian, and Red Hat deem unduly discriminatory toward commercial use.

Open-Core Strategies and Industry Tensions

Several companies have built business models around the open-core strategy, releasing a community edition under a permissive license while keeping an enterprise tier under a restrictive source-available agreement. GitLab is a prominent example: its Community Edition is distributed under the MIT License, while its Enterprise Edition operates under the EE License, which GitLab Inc. itself openly describes as making the product proprietary, closed-source code. Similarly, Mega Ltd. This release came just before former director Kim Dotcom announced his intention to build a fully open-source, non-profit competitor. These examples illustrate how the source-available model has become a deliberate commercial tool, balancing transparency against revenue protection in ways that continue to generate debate across the software community.