What is open source software?

Open source contrasts with proprietary or closed source software applications such as Microsoft Word or Adobe Illustrator. The creator or copyright holder sells the proprietary or closed source software to end users, who are not allowed to edit, enhance or redistribute the product except as specified by the copyright holder.

“Open source” also refers to a community-based approach to creating intellectual property, such as software, through open collaboration, inclusiveness, transparency and frequent public updates.

Open source has become a fundamental pillar of modern software development, especially in regard to the modern enterprise  DevOps model—a set of practices, protocols and technologies used to accelerate the delivery of higher-quality applications and services. By integrating open source tools into DevOps workflows, teams can streamline processes, automate repetitive tasks and foster greater collaboration, ultimately accelerating development and deployment cycles.

According to a study from the Linux Foundation, 70-90% of any given software code base consists of open source elements.¹ Many popular software as a service (SaaS) applications, such as HubSpot and Salesforce, incorporate some level of open source software within their infrastructure. Even traditionally closed ecosystems such as Apple rely on open source tools. For example, many iOS developers use open source libraries and frameworks to make development faster and more efficient

The acceleration of generative AI is propelling this trend: two-thirds of the large language models (LLMs)—the most common foundation models used to build gen AI applications, released in 2023, were open source.²

Until the mid-1970s, IT professionals viewed computer code as implicit in the operation of computer hardware and not unique intellectual property subject to copyright protection. Organizations programmed their own software, and code sharing was a common practice.

The Commission on New Technological Uses of Copyrighted Works was established in 1974. It concluded that software code was a category of creative work suitable for copyright protection. This development fueled the growth of independent software publishing as an industry, with proprietary source code as the primary source of revenue. As personal computing brought applications to every corporate desk and many households, the market for software became intensely competitive. Software publishers also became increasingly alert to infringements of their property rights.

A rebellion against the restrictions and limitations of proprietary software began in 1983. Programmer Richard Stallman chafed at the notion that users could not customize proprietary software however they saw fit to accomplish their work. Stallman felt that “software should be free—as in speech, not beer” and he championed the notion of freely available software for customization.

Stallman founded the Free Software Foundation and would go on to drive the development of an open source alternative to the AT&T-owned Unix operating system, among other applications. He also innovated the first copyleft software license, the GNU General Public License (GPL), which required anyone who enhanced his source code to likewise publish their edited version freely to all.

Eric S. Raymond’s 1997 essay “The Cathedral and the Bazaar” is another watershed in the free software movement. Raymond contrasted the closed, top-down approach typical of proprietary software development, where all development was handled by a core group (which he called The Cathedral), versus open, freely shared public development over the internet (The Bazaar). Shortly after, Netscape Corporation released their Mozilla browser code as open source, and the open source movement gained legitimacy.

Because many felt that Stallman’s term “free software” inaptly emphasized “free of cost” as the principal value of the software, the term “open source” was adopted in 1999. The Open Source Initiative (OCI) was created to advocate for it; the organization also has established ground rules for the industry through the open source definition and hosts compliant open source licenses. Today, the terms free software, open source software, free and open source software and free or libre-open source software all refer to the same thing: software with source code available for public use and customization.

Open source is not to be confused with open standards. Open source refers to software whose source code is freely available for anyone to use, modify and share. An example of this is the Linux operating system, which is developed collaboratively by a global community.

In contrast, open standards are publicly available guidelines that ensure interoperability between different technologies. For instance, Hypertext Transfer Protocol (HTTP) is an open standard that defines how web browsers and servers communicate.

While open source software might implement open standards to ensure compatibility, they are distinct concepts. Open source is about making the software code accessible, while open standards focus on setting rules for how different systems work together.

Open source software now plays a vital role in computing, with open source technologies providing the foundation of the internet, business computing and personal computing. Virtually all computing devices now contain open source code of many types, typically adopted by developers to perform both fundamental operations and more advanced functions.

Some of the most prevalent open source software applications include the following:

• The Linux® operating system, an open source alternative to the Unix operating system

• Mozilla Firefox, a web browser originally based on Netscape Navigator

• LibreOffice, a suite of office productivity apps that rival Microsoft Office

• GIMP (GNU Image Manipulation Program), an open source alternative to Adobe Photoshop

• VLC Media Player, a cross-platform app for viewing videos

Open source programs are also widely used in network, enterprise and cloud computing. The categories of open source software cited by IT professionals as the most common within their organizations’ deployments include:

• Programming languages and frameworks

• Databases and data technologies

• Operating systems

• Git-based public repositories

• Frameworks for artificial intelligence (AI), machine learning (ML), deep learning

The reasons for choosing open source software can vary significantly from person to person and organization to organization. In many cases, end users are completely unaware of the open source programs on their computers or mobile devices. It is also common for end users to download a free application such as the Mozilla Firefox browser or an Android app. These users want the software’s functionality without the intention of rewriting or even looking at the source code.

On the other hand, a company might choose open source software over a proprietary alternative for its low (or no) cost, the flexibility to customize the source code or the large community supporting the application.

Professional or amateur programmers might volunteer their development and testing skills to an open source project, often to enhance their reputation and connect to others in the field. It is now common for organizations to provide paid employees to open source projects to support the vitality of open source software development and help assure high-quality products.

While open source products can spare companies the licensing cost, they can incur other costs—typically for network integration, end-user and IT support, and other services usually included with proprietary software. Still, many organizations consider enterprise open source software to be at least as reliable and secure as proprietary software. They often feel more comfortable with open source solutions because they can inspect the program code and understand exactly what they are adding to their computing infrastructure.

The open source development model encompasses the full range. A vast number of open source programs have originated from solo programmers or small teams of programmers. For example, Guido van Rossum said that he started working on the popular Python programming language because he had free time over the December holiday week in 1989. Similarly, the Apache Kafka web server began with a small group of programmers working together to enhance server software originally written by Robert McCool as an undergraduate in a supercomputing program.

As these and other open source projects like them have matured, they have involved thousands of programmers contributing countless lines of code—testing the software, writing documentation, building the project website and more.

At the other end of the spectrum, Google engineers initiated the Kubernetes container orchestration platform as an open source implementation of technology created internally to balance Google’s server workloads. Google brought the project to the open source community through the creation of a new consortium within the Linux Foundation called the Cloud Native Computing Foundation (CNCF). Since then, thousands of developers have worked on the evolving kernel, including representatives of major computer companies.

Over time, an ecosystem must support open source software projects. Code hosting services such as GitHub, Bitbucket, SourceForge and Google Code provide central repositories, version control and other functions that enable diverse, distributed workgroups to collaborate on and manage open source projects. In a 2023 report, GitHub had registered 100 million developers using its product.³

Some nonprofit organizations, such as the Free Software Foundation and the Open Source Initiative (OCI), have emerged to support and fund the ongoing maintenance of open source projects. Also, many dozens of application-specific foundations, such as the Linux Foundation, support specific open source programs and related projects that support those technologies.

“Open source” and “proprietary” represent alternative approaches to ownership of the intellectual property (IP) embodied within an application. With open source, the IP is intended to benefit the public with no profit motive attached to intellectual property ownership. In contrast, proprietary software monetizes the value of the intellectual property by charging a subscription or proprietary license fee.

However, the idea behind open source software is not primarily an antiprofit or anticapitalism message. Still, in the hands of its user community, the software will naturally achieve its greatest potential by providing greater value to more users.

The largest open source project in history—the internet—was originally used to share academic papers; everything beyond that narrow use case is the result of countless minds envisioning and implementing new possibilities.

While open source software is freely available to the public, it is not in the public domain, a legal intellectual property category devoid of ownership rights. Through an ingenious twist of traditional copyright, open source software creators originated what they named “copyleft,” which permits limitless public usage, alteration and redistribution of the source code, but prevents others from making works based on the code into proprietary, copyrighted software. However, today, there are over 100 different types of open source software licenses, some of which permit derivative works built on open source code to be copyrighted and sold. This expands commercial opportunities for those who create open source software.

Again, Stallman’s GPL stipulated that anyone could rewrite his software however they saw fit, as long as the resulting code was published free for all to use. In this way, the GPL copyleft license created a new kind of quasi-public-domain intellectual property with legally enforceable restrictions imposed by the original copyright holder to protect against others’ later claims of restrictive ownership.

Since then, numerous open source software licenses have been developed; the Open Source Initiative lists over 100 approved open source licenses. Some of these allow proprietary products to be created from open source code.

Open source licenses are sometimes categorized as “permissive”—allowing users to copyright their own works—or “protective,” like copyleft. The MIT and BSD open source licenses are the most commonly used permissive licenses, while GPL remains one of the most widely used protective copyleft licenses. Numerous alternative licenses are compatible with GPL or MIT, meaning that the software code written under this license can be used in another application that uses the GPL or MIT license.

While it seems that the creation of open source software is a high-minded, even charitable enterprise, there is work involved in creating, maintaining and evolving it, and getting this work done is a matter of money. Fortunately, there are a number of ways that open source projects—and companies built around them—can prosper.

One route is through charitable contributions to foundations. Corporations are interested in supporting open source software since it provides such significant functionality at significant cost savings, and they will often contribute funds and provide salaried employees to work on open source projects. However, this primarily provides long-term technology maintenance and does not lead to profits for the open source project.

A more common business model is to charge customers for support and expertise. In 1993, Red Hat® began selling its enterprise redistribution of the Linux operating system, charging customers for support and adding features explicitly aimed at solving problems an enterprise might encounter when deploying a non-curated, continually updated operating system. In 2012, Red Hat became the first open source software company to surpass USD 1 billion in revenue; in 2019, the IBM Corporation acquired Red Hat for USD 34 billion, the largest software acquisition in history.

Over the years, Red Hat has expanded its open source ecosystem beyond Linux, playing a leading role in developing and supporting other key open source projects like Kubernetes and Ansible, which have become integral to its cloud-native and automation solutions.

WordPress, originally a blogging platform, is now widely used for building, managing and hosting websites. WordPress operates as a cloud-based or SaaS platform, and it charges customers tiered subscription fees for web hosting, support and added site functionality (for example, ecommerce capability or SEO tools).

Other open software creators charge nothing for their software but earn significant revenues due to the traffic their software generates. For example, GitHub earns revenues based on advertising on its site; Mozilla Firefox earns revenues from search engines it supports.

According to the Open Source Initiative, open source AI refers to "an AI system that is made available under terms that allow users to freely use the system for any purpose, study how it works, inspect its components, modify it and share it—whether or not the system is changed." This approach emphasizes accessibility, flexibility and transparency, allowing anyone to collaborate on improving the technology.

Open source AI contributes to creating a more democratic and innovative ecosystem. Making AI systems available to the public fosters greater collaboration and accelerates progress in the field. Major organizations, such as IBM (Granite™), Meta (Llama) and Mistral AI, are leading efforts to develop open source AI, providing sophisticated tools to developers and researchers worldwide. For instance, IBM’s AI platform, watsonx.ai™, uses several key AI open source tools and technologies to support innovation and performance.

Large language models (LLMs), advanced AI systems that use deep learning and vast datasets to generate text, convert languages and create various forms of content, can be divided into 2 main categories: proprietary LLMs and open source LLMs. Both types are key to generative AI, a technology that produces new content based on learned patterns and data—text, images or music.

Open source LLMs, in particular, are vital to the generative AI ecosystem because they promote a more transparent, accessible and community-driven approach compared to proprietary models.

Compared to proprietary LLM models, such as Google’s LaMDA and OpenAI’s ChatGPT-3 and GPT-4 , open source LLMs offer distinct benefits. For instance, they allow developers to inspect, modify and improve the models, enabling rapid innovation and customization.

As another example, IBM^® Granite™ AI models, available under Apache 2.0 licenses on Hugging Face and GitHub, deliver comparable performance to larger systems but require far fewer computing resources, showcasing how open source models can provide more efficient alternatives in the generative AI space. Moreover, open source AI provides a cost-effective solution for organizations seeking to fine-tune their generative AI models with proprietary data.     

In 2025, the Chinese company DeepSeek disrupted the AI markets with R1, its large language model that costs just USD 5.6 million to train, a fraction compared to commercial leaders such as ChatGPT. This development demonstrated how open source LLMs can compete with commercial offerings, in this case, using more affordable hardware and fewer advanced microchips.⁵ This shift underscores how open source models contribute to generative AI technology’s democratization.

The open source software market will grow from USD 41.83 billion in 2024 to USD 48.92 billion in 2025 at a compound annual growth rate (CAGR) of 16.9%.³ This rapid growth makes open source security, the practice of managing the security risks associated with using open source software in development and production environments, increasingly critical.

Key security concerns with open source software include potential vulnerabilities in components with unknown origin and lack of design documentation, which can lead to supply chain attacks if compromised libraries are used in a project. 

 As part of their vulnerability management strategy, many organizations use open source intelligence (OSINT), which refers to the gathering and analyzing of publicly available information to assess threats, make decisions or answer specific questions. OSINT is a powerful cybersecurity tool in the broader strategy of open source security because it uses vast amounts of open data to identify threats, track potential risks and ensure that open source software stays secure and reliable.