What is open source software?
Open source software, often shortened to OSS, is software released with source code that people can inspect, use, change, and share under the terms of an open source license.
A useful definition: open source software is software whose license gives users the right to access the source code, run the program, study how it works, modify it, and redistribute original or modified versions.
That license is the important part. A GitHub repository that lets you read code but does not include an open source license is not automatically open source. Public visibility is not the same as legal permission. Open source depends on rights, not just access.
This matters because software is protected by copyright by default. Without a license, users usually do not have permission to copy, modify, distribute, or reuse the code. An open source license changes that by granting those permissions in advance.
What is open source?
The phrase "open source" came from software, but the broader idea is about making the design of something available so others can inspect, improve, adapt, and share it. Opensource.com summarizes the general idea as something people can modify and share because its design is publicly accessible.
In software, "the design" is mostly the source code. In other fields, the same philosophy can apply to hardware designs, data sets, documentation, AI models, educational materials, or scientific methods. For software, though, open source has a specific legal and practical meaning - it is not just a vibe, a marketing label, or a synonym for "transparent."
What is source code?
Source code is the human-readable text that programmers write to create software. It might be written in languages such as Python, JavaScript, Go, Rust, Java, C, C++, PHP, Ruby, or TypeScript.
Most users never see source code. They interact with finished applications: a browser, a password manager, a database, an operating system, a note-taking app, an analytics dashboard, or a design tool. But behind every application is code that defines what the program does.
If the source code is closed, users must trust the vendor about how the software works. If it is open, users, developers, security researchers, companies, governments, and independent maintainers can inspect it. That does not mean every user reads the code - most do not. The point is that someone can. Open source turns blind trust into verifiable trust.
What makes software truly open source?
To be truly open source, software needs more than a public repository - it needs an open source license. The Open Source Definition requires that a license allow free redistribution, include or provide access to source code, allow modifications and derived works, avoid discrimination against people or fields of use, apply rights to downstream recipients, and stay technology-neutral.
In plain English, open source software should let you:
- Use it for personal, academic, nonprofit, government, or commercial purposes.
- Read the source code.
- Modify the code.
- Share the original software.
- Share your modified version.
- Use it without asking the original author for special permission.
This is why "free for personal use," "non-commercial only," "view but do not modify," and "modify but do not redistribute" are not normal open source terms. Those may be source-available or freeware models, but they are not open source in the standard sense.
Open source vs proprietary software
Proprietary software is controlled by its owner, who usually decides who may use it, how it may be installed, whether it may be copied, what features exist, how much it costs, and whether users can access the code. Open source works differently: the author still owns the copyright, but grants broad permissions through a license.
| Question | Open source software | Proprietary software |
|---|---|---|
| Can you inspect the source code? | Usually yes | Usually no |
| Can you modify the software? | Usually yes, per the license | Usually no |
| Can you redistribute it? | Usually yes, per the license | Usually restricted |
| Can you self-host it? | Often yes, if built for server use | Often no |
| Can a vendor remove your access? | Harder if you run your own copy | Easier if it is SaaS-only |
| Is it always free of cost? | No | No |
| Does it require maintenance? | Yes | Yes, often hidden behind support |
The important difference is control. Proprietary software asks you to trust and rent. Open source software gives you the option to inspect and own.
Open source vs freeware vs source-available
Freeware costs nothing to use but can still be closed source - a company can release a free app without showing the code or allowing changes. Source-available software lets you view the code, but the license may not grant full open source rights (for example, "view but do not use commercially," or "self-host only below a revenue threshold"). Open source may also be free of charge, but price is not the defining feature. The license is.
| Model | Source visible? | Modify? | Redistribute? | Commercial use? |
|---|---|---|---|---|
| Open source | Yes | Yes | Yes | Yes |
| Source-available | Yes | Sometimes | Often no | Often restricted |
| Freeware | No | No | Usually no | Sometimes |
If a license restricts fields of use, prohibits commercial use, or blocks redistribution of modified versions, it is probably not open source under the standard definition.
What is open source development?
Open source development is building software in a way that lets outside users and contributors take part. It usually happens in public repositories, issue trackers, mailing lists, chat rooms, forums, and pull requests. It can be run by a single maintainer, a volunteer team, a startup, a large company, a nonprofit foundation, a standards body, or a loose community. GitHub frames it around transparency, collaboration, and decentralization: code is developed in public, contributors can review and patch it, and development can happen outside one company.
So "open source development" does not always mean "everyone votes on everything." It means the code and the collaboration process are open enough that people can inspect, report, propose, fork, patch, and learn.
How open source software works
A typical open source project has a public repository, a license file that defines user rights, documentation, an issue tracker, pull or merge requests, maintainers who review and release, a release process, and a support channel. The workflow usually looks like this:
- Someone publishes code under an open source license.
- Users install it and report bugs or request improvements.
- Developers submit fixes or new features.
- Maintainers review the changes.
- Accepted changes become part of future releases.
- Companies or individuals build services, hosting, plugins, or support around it.
This is how open source technology scales: many people can observe the code, test it in different environments, report problems, and contribute fixes.
Common open source licenses
Open source licenses vary. Permissive licenses allow broad reuse with minimal obligations. Copyleft licenses require that modified or redistributed versions stay under the same or a compatible license.
| License | Type | In short |
|---|---|---|
| MIT | Permissive | Minimal obligations; easy commercial adoption |
| Apache 2.0 | Permissive | Permissive, with an explicit patent grant |
| BSD (2/3-clause) | Permissive | Minimal, attribution-based |
| GPL | Copyleft | Redistributed modifications must stay open |
| LGPL | Weak copyleft | Lets proprietary apps link the library |
| MPL | Weak copyleft | File-level copyleft |
| AGPL | Network copyleft | Also covers software offered over a network |
For users the lesson is simple: always check the license before adopting open source software. "Open source" does not mean "no rules" - it means the rules are published in advance.
Open source software examples
Open source software appears in almost every layer of modern computing - browsers, operating systems, databases, office suites, creative tools, and analytics platforms. Here are a few well-known projects (each links to its page in the directory):
FirefoxBrowser
LibreOfficeOffice suite
GIMPImage editor
Blender3D creation
WordPressCMS
PostgreSQLDatabase
MariaDBDatabase
VLCMedia player
OBS StudioStreaming
MetabaseAnalytics
DrupalCMS platform
Apache KafkaEvent streamingOther major examples have no dedicated page here yet: GNU/Linux (the operating system family), Kubernetes (container orchestration), Docker tooling, Node.js (a JavaScript runtime), MySQL, and Nextcloud (file sync and collaboration). Open source is not limited to developer tools - it also covers CRMs, CMSs, project management apps, image editors, video editors, and self-hosted replacements for commercial SaaS.
What is an open source operating system?
An open source operating system is an OS whose source code is available under open source licenses, so users and developers can inspect, modify, compile, redistribute, and build on it. The most important example is GNU/Linux. People often say "Linux" to mean complete systems such as Ubuntu, Debian, Fedora, Arch, Linux Mint, Rocky Linux, or Alpine - strictly, Linux is the kernel, and a distribution bundles the kernel with utilities, package managers, desktop environments, drivers, libraries, and applications.
Operating systems matter because the OS controls the machine. If you can inspect and modify it, you have far more control over security, privacy, performance, deployment, hardware support, and long-term maintenance - which is why open source operating systems dominate so many server, cloud, embedded, and infrastructure environments.
What is an open source platform?
An open source platform is a larger foundation for building, running, deploying, or extending other software. Examples include Kubernetes for orchestrating containers, WordPress for publishing websites, Drupal for content-heavy systems, Node.js for server-side JavaScript, Apache Kafka for event streaming, PostgreSQL for relational data, and OpenStack for cloud infrastructure.
A platform is usually more than a single app - it has an ecosystem of plugins, extensions, APIs, integrations, hosting providers, consultants, and support. Many open source solutions become valuable not just because the code is open, but because the ecosystem around it is strong.
Open source products and services
Open source products are finished tools, apps, platforms, or services built around open source software: a downloadable desktop app, a CLI tool, a self-hosted web app, a database, an API gateway, a CMS, a password manager, an observability stack, or a commercial cloud service. Some are community-run; others are built by companies with open-core, hosted SaaS, consulting, or enterprise models.
Open source software services are the commercial or professional layer on top: managed hosting, enterprise support, security patching, custom development, migration, training, compliance and license review, managed databases, and SLA-backed operations. A company might use PostgreSQL for free but pay for managed hosting, or use Kubernetes for free but pay for a managed platform. This is one of the healthiest business models in open source: charge for operational value, not artificial restriction.
Why use open source software?
The main benefits are control, transparency, flexibility, cost efficiency, portability, community, and resilience.
Open source software gives users more control over their tools. You can run the software yourself, inspect how it works, change the parts you dislike, remove unwanted behavior, and keep using a version even if a vendor changes strategy. This matters most for teams that do not want their workflows, data, and infrastructure trapped inside a proprietary SaaS product.
Open source code can be audited. That does not automatically make it secure, but it makes inspection possible. With closed source software you must rely on vendor claims. With open source software, independent researchers, companies, governments, and users can examine the code and verify how it actually behaves.
Open source software can be adapted. Developers can add or remove features, integrate with internal systems, localize interfaces, improve performance, or patch bugs without waiting for a vendor roadmap. That makes it especially valuable for technical teams with unusual requirements.
Many open source tools do not charge per user, which can cut costs sharply for teams replacing expensive per-seat SaaS. But zero license cost is not zero total cost. Hosting, maintenance, updates, backups, security, training, and support still add up.
If the code, data formats, and deployment model are open, you have more ways to leave a bad vendor or keep using a tool after its commercial terms change. This is one of the strongest arguments for open source: not that it is free, but that you keep your exit options.
More people can inspect, test, and patch open code. But the benefit is conditional: auditability is not the same as an audit. A neglected project with few maintainers can be risky, while a well-maintained project with active review and a real security process can be extremely robust.
Open source projects often grow communities of users, maintainers, contributors, translators, consultants, and companies. That community produces documentation, tutorials, integrations, bug reports, and institutional knowledge that no single vendor could build alone.
If a proprietary vendor shuts a product down, users can lose access. If an open source maintainer steps away, the community can fork the project, continue maintenance, or preserve old versions. It is not a survival guarantee, but it improves the odds that important software outlives its original creator.
The limits and risks of open source software
Open source is powerful, but it is not magic, and bad adoption is common. Open code can be inspected, but someone must actually inspect it. Many projects are maintained by volunteers with limited time, some dependencies are abandoned, some packages get compromised, and some vulnerabilities go unnoticed for years.
of audited codebases contained open source components - open source is no longer niche, it is the default substrate of modern software.
The right conclusion is not "avoid open source" - that is unrealistic. The right conclusion is "manage open source deliberately." A few other realities are worth naming:
- Not always cheaper
Open source cuts license fees, but total cost includes hosting, maintenance, backups, security updates, monitoring, migration, training, customization, support, and internal developer time. For a small team a paid SaaS tool can be cheaper; for a larger org, self-hosting can be far more economical and strategically safer.
- User experience varies
Some open source tools are beautifully designed; others are rough. Do not assume open source means bad UX - and do not assume it means good UX. Evaluate the product.
- License compliance matters
Some licenses require attribution or notices; some require source distribution for modified versions; some network-copyleft licenses affect hosted software. For companies shipping software, license review matters.
- Maintenance risk is real
A project can look popular but be poorly maintained. Before adopting a tool, check recent commits and releases, issue response quality, a security policy, documentation, license clarity, community health, and dependency freshness.
How to choose open source software
Choosing open source is not just about finding a free alternative - it is about choosing a tool you can trust, operate, and keep using. Work through this checklist:
For non-technical users, the best first question is: "What proprietary tool am I trying to replace?" Then look for open source alternatives by category. For technical users, the better question is: "What trade-off am I willing to own - hosting, maintenance, customization, compliance, or vendor dependency?"
Open source software for businesses
Businesses use open source to reduce costs, increase flexibility, accelerate development, and cut dependence on a single vendor. Common cases include replacing expensive SaaS, building internal tools, running infrastructure, managing databases, creating analytics dashboards, hosting documentation, deploying AI workflows, managing identity and access, and improving privacy and data control.
The business case is strongest when open source gives you strategic control over an important workflow, and weakest when the team lacks the ability or discipline to run the software safely. A useful rule: use open source when ownership matters; use managed services when operations matter more than control; and avoid proprietary lock-in when the tool becomes mission-critical.
Open source software for developers
For developers, open source is both a toolset and a learning system. It lets you read real production code, learn architecture patterns, contribute bug fixes, build a public reputation, reuse libraries, avoid reinventing basic infrastructure, collaborate with maintainers, and understand licenses and governance.
Modern software depends heavily on open source packages, frameworks, languages, databases, runtimes, and deployment tools - so most developers are open source users even if they never contribute. The next step is becoming a responsible participant: read licenses, report bugs well, contribute documentation, sponsor maintainers when you can, and upstream fixes instead of maintaining private patches forever.
Why open source technology matters now
Open source matters because the world runs on software, and software increasingly runs on shared infrastructure. The browser, the server, the database, the language, the container runtime, the AI framework, the package manager, the OS, the encryption library, the CMS, and the deployment pipeline often include open source components.
That creates two realities at once. Open source is one of the greatest coordination mechanisms in technology: it lets us reuse infrastructure instead of rebuilding everything from scratch. But it also creates shared risk - if everyone depends on the same packages, maintainers, registries, and build systems, vulnerabilities and supply-chain attacks can spread widely. The mature view is neither romantic nor cynical: open source is infrastructure, so treat it like infrastructure.
How Open Source Tools helps
Open Source Tools is built for people who want software they can own, run, and audit themselves instead of renting another closed SaaS product. The hard part of open source is no longer finding random projects - it is choosing well.
The directory organizes open source apps into categories and maps them to the proprietary tools they can replace. It surfaces practical signals - license, programming language, and GitHub activity - so you can judge a project before committing to it.
Frequently asked questions
What is open source software?+
Open source software is software released under a license that lets people use, inspect, modify, and redistribute its source code. It is defined by permissions, not just by whether the code happens to be visible.
What is open source?+
Open source means the underlying design of something is available for others to inspect, modify, and share. In software, that design is the source code, and the rights are granted through an open source license.
What is open source code?+
Open source code is source code released under an open source license. Users can read it, learn from it, modify it, and redistribute it according to the license terms.
Is open source software free?+
Often, but not always. Many open source tools are free to download and use, but open source is not defined by price. It is defined by the right to use, inspect, modify, and share the code. Companies can charge for hosting, support, enterprise features, consulting, or managed services.
Is freeware the same as open source software?+
No. Freeware costs nothing to use, but the source code may still be closed. Open source software gives users rights to inspect, modify, and redistribute the code.
Is source-available software the same as open source software?+
No. Source-available software lets you view the code, but the license may restrict modification, redistribution, commercial use, or production use. True open source software must provide broader rights.
What is open source development?+
Open source development is a model where code, issues, discussions, and contributions are often handled publicly. Developers can inspect the code, report bugs, propose changes, fork the project, and collaborate with maintainers.
What is open source programming?+
Open source programming usually means writing, using, or contributing to software released under an open source license. It can involve building projects, fixing bugs, writing documentation, creating plugins, or using open source libraries in larger applications.
What is an open source operating system?+
An open source operating system is an OS whose source code is available under open source licenses. GNU/Linux distributions such as Ubuntu, Debian, Fedora, and Arch are common examples.
What is an open source platform?+
An open source platform is a broader software foundation for building or running other software. Examples include Kubernetes, WordPress, PostgreSQL, Node.js, Apache Kafka, and OpenStack.
What are examples of open source software?+
Examples include GNU/Linux, Firefox, LibreOffice, GIMP, Blender, WordPress, PostgreSQL, Kubernetes, VLC, OBS Studio, Nextcloud, and Metabase, plus many developer tools, databases, CMSs, and self-hosted apps.
What are the main open source benefits?+
The main benefits are control, transparency, flexibility, lower licensing costs, reduced vendor lock-in, auditability, community, and long-term resilience.
Is open source software safe?+
It can be very safe, but it is not automatically safe. Open code can be audited, but projects still need active maintenance, security updates, dependency management, and responsible users.
Can businesses use open source software?+
Yes. Open source licenses generally allow commercial use, though companies must still follow the license terms. Businesses use open source for infrastructure, internal tools, databases, analytics, AI, content management, security, and automation.
Can you sell open source software?+
Yes. Open source licenses can allow selling software, support, hosting, services, or enterprise versions. The key is complying with the license terms.
What does "opensource software" mean?+
"Opensource software" is just a common compressed spelling of "open source software." The standard spelling is two words: open source.