What Is Open Source Software and Why Does It Matter?

Many everyday tools, from web servers to smartphone operating systems, are built on open source software. The term refers to software whose source code is published and can be used, studied and changed under a licence.

Key takeaways

• Open source software makes its source code available under a licence.
• Licences set the rules for use, modification and sharing.
• Well-known examples include Linux, Firefox and the Python language.
• Open source is not the same as free of cost or without rules.
• Many companies use and contribute to open source projects.

What "open source" means

Source code is the human-readable instructions that programmers write. Proprietary software is usually distributed only as compiled programs, with the source kept private. Open source projects publish the code so people can read it, run it, adapt it and share their changes. The Open Source Initiative maintains a widely used definition of what qualifies, including free redistribution and access to source code.

Licences

Open source software is released under a licence that spells out the conditions. Permissive licences, such as MIT and Apache 2.0, allow reuse with few requirements, usually keeping the copyright notice. Copyleft licences, such as the GNU General Public License, require that modified versions that are distributed also be shared under the same terms. Choosing and following the right licence matters, because ignoring its terms can create legal problems.

Well-known examples

The Linux kernel runs on most web servers, many phones and supercomputers. Web browsers such as Firefox, the Python and Rust programming languages, the WordPress publishing platform and the Git version control system are all open source. Android is built on open source components, though phone makers add proprietary parts.

How projects are run

Open source projects are maintained by volunteers, companies or both. Contributors suggest changes, often called pull requests, and maintainers review and merge them. Public issue trackers let anyone report bugs. Some projects are supported by foundations that handle legal and financial matters.

Benefits

Open code can be inspected by many people, which can help find and fix bugs, although having code visible does not automatically make it secure. Users can adapt software to their needs, avoid being locked in to one vendor and learn from real-world code. Organisations often save development time by building on existing components.

Challenges

Maintaining a project takes effort, and widely used libraries are sometimes kept running by very few unpaid volunteers. Security problems in popular components can affect many products at once, so companies are paying more attention to funding, auditing and tracking the open source pieces they depend on.

Open source versus free

"Free software" in the original sense refers to freedom to use, change and share, not necessarily zero price. Open source software is often free of charge, but companies may sell support, hosting or enhanced versions.

Famous projects and their stories

The modern open source movement has deep roots. In 1983, Richard Stallman launched the GNU project to build a free operating system, and the Free Software Foundation followed. In 1991, the Finnish student Linus Torvalds announced a hobby kernel that became Linux, and the combination of GNU tools and the Linux kernel became a widely used operating system. The Apache web server helped power the early web, the Mozilla project grew out of the Netscape browser, and Torvalds created the Git version control system in 2005 after a dispute over a tool used for Linux development. Today, countless programming languages, databases and tools are open source.

Choosing a licence

If you publish code, the licence is not a minor detail. The MIT and BSD licences are short and permissive, letting others use the code freely if they keep the copyright notice. Apache 2.0 is also permissive and adds an explicit grant of patent rights. The GNU General Public License requires that anyone who distributes a modified version shares the source under the same licence. Without any licence, the default is that others cannot legally reuse your code. For important projects, it is wise to read the licence texts carefully or ask a lawyer.

Open source in everyday devices

Open source runs in places most people never see. Home routers, smart TVs, cars, medical devices and phones often rely on open source components such as the Linux kernel and open libraries for networking, encryption and media. Websites often run on open source web servers and content management systems. When you use a device, there may be dozens or hundreds of open source packages inside it, usually listed in a licences section of the settings.

How open source projects make money

People sometimes assume open source means no money. In practice, companies and developers earn from it in several ways: selling support contracts, offering hosted services, building commercial products on top of open projects, and sponsoring maintainers. Foundations such as the Linux Foundation and the Apache Software Foundation coordinate funding and governance. Individual developers can receive donations or sponsorship, though many maintainers still work unpaid in their spare time.

Security lessons

Open code can be reviewed, but that does not guarantee that anyone has looked at every part. In 2014, a flaw called Heartbleed was found in OpenSSL, a library used to secure much of the web, and it showed how a small, underfunded project could carry enormous risk. In 2021, the Log4Shell vulnerability in a common Java logging library affected huge numbers of systems. These events led to more funding, better auditing and the practice of keeping a software bill of materials, a list of the components in a product.

Frequently asked questions

Can I use open source software at work?

Usually yes, but check the licence terms and your organisation's policies.

Is open source software safe?

It can be, but safety depends on how well a project is maintained and updated, not simply on whether the code is public.

How can I contribute?

You can report bugs, improve documentation, translate text or submit code changes to a project you use.

Can I use open source software commercially?

Usually yes, as long as you follow the licence terms. Permissive licences allow almost any use. Copyleft licences allow commercial use too, but they may require you to share your changes if you distribute the software.

Who pays for open source?

A mix of companies, foundations, governments and individual donors, along with a great deal of volunteer time. Large companies that depend on open source increasingly pay developers or sponsor projects, though funding is still uneven.

Can I trust open source software?

Trust depends on the project. Look at whether it is actively maintained, how quickly security problems are fixed, how many people contribute and whether it has been independently reviewed. Popular, well-maintained projects are often very reliable.

Sources and further reading

• Open-source software (Wikipedia)
• Open Source Initiative