What Open Source Is

Beyond Code on GitHub

Making a repository public does not make it open source. Open source is a specific legal and philosophical framework that grants users explicit rights over software. A public repository with no license is "source-available" at best — you can read the code, but you cannot legally use, modify, or distribute it.

The term "open source" was coined in 1998 by Christine Peterson and adopted by the Open Source Initiative (OSI). But the movement predates the name by decades. Richard Stallman's GNU Project, started in 1983, established the principles of free software. The open source label was a deliberate rebranding to make the concept palatable to businesses that were allergic to the word "free."

Understanding what open source actually is — and what it is not — matters because the distinction has legal, business, and community consequences.

The Four Freedoms

The Free Software Foundation defines four essential freedoms that software must grant to qualify as free software:

Freedom 0: The freedom to run the program for any purpose
Freedom 1: The freedom to study how the program works and change it (requires source code access)
Freedom 2: The freedom to redistribute copies
Freedom 3: The freedom to distribute copies of your modified versions

The Open Source Definition, maintained by the OSI, expresses similar ideas through ten criteria, including free redistribution, source code availability, and permission for derived works. In practice, the two definitions overlap almost entirely. The differences are philosophical rather than practical.

These freedoms are not suggestions. They are encoded in licenses. When you release code under the MIT license, you legally grant all four freedoms. When a company releases code under a "community license" that prohibits commercial use, that is not open source — regardless of what their marketing page claims.

Open Source vs Free Software vs Source-Available

These three terms describe different things, and conflating them causes confusion:

Free Software

Free software emphasizes user freedom as a moral imperative. The Free Software Foundation (FSF) argues that proprietary software is inherently unethical because it denies users control over their own computing. The GPL family of licenses embodies this philosophy — if you modify GPL software and distribute it, your modifications must also be free software. This is copyleft: freedom that propagates.

Open Source

Open source emphasizes practical benefits. The OSI defines open source through the Open Source Definition, which focuses on license terms rather than philosophy. Open source advocates argue that open development produces better software — more eyes on the code, faster bug fixes, broader testing. The Apache 2.0 and MIT licenses are open source but not copyleft.

Source-Available

Source-available means the source code is published but the license restricts what you can do with it. Examples include:

Elastic License 2.0 (Elasticsearch, after the AWS dispute): you can use and modify the code, but you cannot offer it as a managed service
Business Source License (MariaDB, CockroachDB, HashiCorp): source is available, but commercial use is restricted for a time period
Server Side Public License (MongoDB): imposes obligations so broad that the OSI rejected it as open source

These licenses exist because companies watched AWS take their open source projects, offer them as managed services, and capture the revenue. The response — restricting cloud providers — is understandable, but it is not open source by any standard definition.

The Open Source Ecosystem

Open source is not just code. It is an ecosystem of interconnected components:

Projects

A project is more than a repository. It includes the code, the documentation, the issue tracker, the CI pipeline, the release process, and most importantly, the community. Linux is not just a kernel — it is thousands of contributors, dozens of subsystem maintainers, a mailing list culture, and a release process refined over 30+ years.

Contributors

Contributors range from first-time documentation fixers to full-time kernel developers. Most open source projects follow a power-law distribution: a small number of people do the vast majority of the work. The Linux kernel has received contributions from over 20,000 developers, but a core group of a few hundred does most of the heavy lifting.

Foundations

Foundations provide legal, financial, and organizational infrastructure. The Apache Software Foundation hosts over 350 projects. The Linux Foundation houses the Linux kernel, Kubernetes, Node.js, and dozens of other critical projects. The CNCF (Cloud Native Computing Foundation) governs the cloud-native ecosystem. These organizations handle trademarks, accept donations, employ maintainers, and shield individual contributors from legal risk.

Companies

Companies are the largest contributors to open source by volume. Google created and maintains Kubernetes, TensorFlow, and Go. Meta developed React, PyTorch, and Llama. Microsoft contributes to VS Code, TypeScript, and the Linux kernel. Red Hat built a billion-dollar business on enterprise Linux support. These companies contribute for strategic reasons — to commoditize complements, attract talent, and influence standards.

Why Open Source Won

In most categories of infrastructure software, open source is the default:

Linux

Linux runs on over 90% of public cloud instances, all of the world's top 500 supercomputers, and most embedded devices. It powers Android. It won against proprietary Unix variants (Solaris, AIX, HP-UX) not because it was technically superior at the start, but because anyone could use, modify, and distribute it. Companies that needed a custom kernel could build one. Cloud providers that needed a lightweight VM host could strip it down. That flexibility compounded over decades.

Kubernetes

Kubernetes is the standard container orchestration platform. Google open-sourced it in 2014, donated it to the CNCF, and it rapidly displaced proprietary alternatives. Every major cloud provider now offers a managed Kubernetes service. The open source model meant that AWS, Azure, and GCP all contributed to and competed on the same codebase, creating a shared standard that no single vendor controls.

PostgreSQL

PostgreSQL has steadily gained market share against Oracle Database for decades. It is free to run, free to modify, and free to embed in commercial products. Companies like Supabase, Neon, and Crunchy Data have built businesses on top of PostgreSQL without paying license fees to anyone. The permissive license (PostgreSQL License, similar to BSD) means no vendor lock-in.

React

React dominates frontend development. When Facebook open-sourced it in 2013, there were dozens of competing UI frameworks. React won because open source meant any developer could use it, any company could adopt it, and a massive community formed around it, producing libraries, tools, tutorials, and job listings that reinforced its dominance.

The Business of Free Software

"If it's free, how do you make money?" is the most common question about open source. The answer depends on the model:

Support & Services

Red Hat sells enterprise support, certifications, and consulting for Red Hat Enterprise Linux. The software is free. The expertise and the guarantee of stability are not. This model works for complex infrastructure software that enterprises need help running.

Open Core

The core product is open source; advanced features (usually enterprise administration, security, or compliance tools) are proprietary. GitLab, Grafana, and Elastic follow this model. The open source version attracts users; the proprietary features convert some of them to paying customers.

Cloud / SaaS

Companies host the open source software as a managed service. MongoDB Atlas, Confluent Cloud (Kafka), and Vercel (Next.js) follow this pattern. The value proposition is not the software itself but the operational burden they remove.

Dual Licensing

The software is available under a copyleft license (like AGPL) for free, and under a commercial license for companies that do not want copyleft obligations. MySQL pioneered this model. Qt uses it today.

Consulting & Custom Development

Small projects and independent developers often fund their work through consulting engagements related to their open source project. The project demonstrates expertise; clients pay for customization and integration.

None of these models is universally viable. Many open source projects are unfunded. Many maintainers burn out. The sustainability problem is real, and we will cover it in later topics.

Common Pitfalls

Confusing "Public" with "Open Source"

A repository with no license file grants no rights. Under default copyright law, the author retains all rights. If you find a public repository with no license, you cannot legally copy, modify, or distribute the code. Always add a license before publishing.

Treating Source-Available as Open Source

When Terraform switched from the Mozilla Public License to the Business Source License in 2023, the community forked it as OpenTofu. The BSL is not open source. Using source-available software carries different risks than using truly open source software — the vendor can change terms, restrict use cases, or revoke access in future versions.

Assuming Open Source Means No Cost

Open source software is free to acquire but not free to operate. Running PostgreSQL costs compute, storage, backups, monitoring, upgrades, and the salary of someone who understands it. The license cost is zero; the total cost of ownership is not.

Ignoring the Community

Using open source without ever filing a bug report, contributing a fix, or even reading the changelog is like drinking from a well and never maintaining it. The software does not maintain itself. If your business depends on an open source project, contributing back is not charity — it is risk management.

Key Takeaways

Open source is a legal framework defined by licenses that grant specific freedoms — not merely code that happens to be visible.
Free software, open source, and source-available are distinct concepts with different implications for users and developers.
The open source ecosystem includes projects, contributors, foundations, and companies, each playing a different role.
Open source won in infrastructure (Linux, Kubernetes, PostgreSQL) because unrestricted use and modification create compounding network effects.
Open source businesses make money through support, open core, cloud hosting, dual licensing, and consulting — not by selling the code itself.
Always add a license to your public repositories. No license means no rights for anyone else.