Open source software is code that anyone can read, modify, and share

Open source software is a program where the underlying code — the instructions that make it work — is publicly available for anyone to see and change. Unlike commercial software you buy from a company, open source projects publish their source code so programmers can inspect it, fix problems, improve it, and build new versions. You typically do not pay money for open source software, and you are usually allowed to use it however you want, including for business purposes.

The key difference from regular paid software is transparency. When you buy Microsoft Word or Adobe Photoshop, you cannot see how the program actually works — the company keeps that code private. With open source software like LibreOffice or GIMP, the code is right there. This means you can verify that the program does what it claims, spot security problems yourself, and modify it to fit your exact needs instead of waiting for the company to release an update.

Key Takeaways

  • Open source software publishes its code publicly so anyone can read it, modify it, and redistribute it under a license that sets the rules.
  • You do not pay for open source software, but you must follow the license terms, which vary — some require you to share your changes, others do not.
  • Common open source programs include Firefox (web browser), LibreOffice (office suite), and VLC (media player), all free and available for Windows, Mac, and Linux.
  • Open source software is maintained by volunteers, companies, or both working together, so support and update speed depend on who is behind each project.
  • The license you receive with open source software determines what you can legally do with it — reading the license matters because different open source projects have different rules.

How open source licenses control what you can do

Open source software comes with a license — a legal document that explains what you are allowed to do with the code. The license is not optional; it is the contract that makes the software open source in the first place. Different open source projects use different licenses, and the rules vary significantly.

Some licenses, like the GPL (General Public License), require that if you modify the software and share it with others, you must also share your changes under the same license. This is called copyleft. Other licenses, like the MIT License or Apache License, let you modify the code and keep your changes private — you can use the software in a closed commercial product without sharing your improvements. A third group, like the BSD License, sits somewhere in between. The license you receive tells you whether you can use the software commercially, whether you must publish your changes, and whether you can combine it with other software.

Common open source software you may already use

Open source programs run on millions of computers and devices. Firefox is an open source web browser that competes directly with Chrome and Edge. LibreOffice is a free office suite (word processor, spreadsheet, presentation software) that works like Microsoft Office. VLC is a media player that plays almost any video or audio file. Audacity is a free audio editor. GIMP is a free image editor similar to Photoshop. All of these are completely free, do not require a license key, and do not phone home to a company to verify you are using them legally.

On the server side and in business, open source is even more dominant. Linux is an open source operating system that powers most web servers, cloud infrastructure, and Android phones. Apache is an open source web server that runs a large portion of the internet. PostgreSQL and MySQL are open source databases. Many companies build their entire business on open source software — they do not pay licensing fees, and they can modify the code to fit their operations exactly.

Who maintains open source projects and how they stay updated

Open source software is maintained by different groups depending on the project. Some projects are run by a single volunteer who updates it in their spare time. Others are backed by large companies — Red Hat maintains much of the Linux ecosystem, Mozilla funds Firefox, and Google contributes heavily to Android. Many projects have a mix: a core team of maintainers (some paid, some volunteer) plus hundreds of community contributors who submit fixes and features.

Updates and bug fixes happen when someone in the community identifies a problem, writes a fix, and submits it for review. This process is usually faster than commercial software for security problems — if a vulnerability is discovered, dozens of programmers may already be working on a patch. However, updates for less critical features can move slowly or stall entirely if the project loses active maintainers. You should check how recently a project was updated before relying on it; a project that has not been touched in three years may have unpatched security problems.

The difference between open source and free software

The terms "open source" and "free software" are related but not identical. Free software means the software respects your freedom — you can run it, modify it, and share it. Open source means the code is publicly available. In practice, most projects are both, but the emphasis is different. The free software movement focuses on user freedom and philosophy. The open source movement focuses on practical benefits like code quality and security.

There is also "freeware," which is completely different. Freeware is software you do not pay for, but the code is not public and you cannot modify it — it is just free to use. Freeware is not open source. When you see "free" in software, check whether the code is actually public before assuming it is open source.

Why companies use open source software

Businesses adopt open source for several reasons. First, there are no licensing fees — a company can deploy the same software to thousands of computers without paying per seat. Second, they can modify the code to fit their exact workflow instead of adapting their process to match the software. Third, they can audit the code themselves to verify security and performance, rather than trusting a vendor's claims. Fourth, they avoid vendor lock-in — if the company behind the software goes out of business or stops supporting it, the code is still available and the community can continue maintaining it.

Large technology companies like Google, Amazon, Meta, and Microsoft now contribute to open source projects and release their own open source software. This is a shift from the 1990s and 2000s, when commercial software companies treated open source as a threat. Today, open source is mainstream in enterprise software, cloud infrastructure, and development tools.

Open source software and security

A common misconception is that open source software is less secure because the code is public — the logic being that hackers can see the vulnerabilities. In practice, the opposite is often true. When code is public, security researchers and the community can spot problems quickly. Vulnerabilities in open source projects are usually patched faster than in closed commercial software because the fix does not have to go through a company's release cycle.

However, open source security depends on the project's maintenance level. A well-maintained project with active developers and security reviews is typically more secure than a dormant one. Before using an open source project in a production environment, check when it was last updated, how many active maintainers it has, and whether it has a documented security policy for reporting vulnerabilities.

Frequently Asked Questions

Can I use open source software at work or in my business?

Yes, most open source licenses allow commercial use. However, read the specific license first — some require you to share your modifications, while others do not. If you modify open source code and sell a product that includes it, the license determines whether you must publish your changes.

Do I need to credit the original author if I use open source software?

Most open source licenses require attribution — you must include a notice that says where the code came from and who wrote it. Some licenses are stricter about this than others. Check the license file that comes with the software to see what is required.

What happens if an open source project stops being maintained?

If a project becomes inactive, you can still use the existing version, but it will not receive security updates or new features. Some projects are forked — the community takes the code and continues it under a new name. Others simply become legacy software that works but is no longer developed.

Is open source software really free, or do I have to pay eventually?

Open source software itself is free — you do not pay for the program. Some companies offer paid support, training, or hosting services built around open source software, but the software code is always free. You can use it without paying anything.

How do I know if software is actually open source?

Look for a license file in the software's documentation or repository. Common open source licenses include GPL, MIT, Apache, and BSD. If the project publishes its source code on GitHub, GitLab, or a similar platform and includes a recognized open source license, it is open source. If you cannot find the source code or a license, it is not open source.