Open source software is code that anyone can read, modify, and share
Open source software is a program where the original code — the instructions that make it work — is published openly for anyone to see, change, and redistribute. Unlike proprietary software, where the company keeps the code secret and controls how you use it, open source lets you examine exactly what the program does. You can modify it for your own needs, share your improvements with others, or build something new on top of it.
The key difference from the licensing and set up systems you read about earlier is that open source software typically has no set up requirement, no license key, and no company controlling whether you can use it. Instead, it operates under a license agreement that spells out what you can and cannot do with the code. The most common licenses — like the GNU General Public License (GPL) and the MIT License — let you use the software for free, but they have different rules about whether you must share your changes back with the community.
Key Takeaways
- Open source software publishes its code openly, so you can read it, modify it, and share it under the terms of a license agreement.
- Most open source software is free to read and use, with no set up key or company permission required.
- Different open source licenses have different rules — some require you to share improvements back, others do not.
- Common open source programs include Firefox, LibreOffice, VLC media player, and the Linux operating system itself.
- Open source does not mean uncontrolled or unsafe; many projects have maintainers who review changes and fix security problems.
How open source licenses control what you can do
An open source license is a legal agreement that comes with the code. It tells you what you are allowed to do — use it, modify it, sell it, distribute it — and what you must do in return. The license is what makes open source "open" rather than just abandoned code.
The GPL (GNU General Public License) is the most restrictive common license. If you modify GPL software and share it with others, you must release your changes under the GPL as well. This means you cannot take GPL code, improve it, and then sell it as closed-source software. The GPL is designed to keep improvements flowing back to the community.
The MIT License and Apache License 2.0 are more permissive. They let you modify the code and use it in closed-source commercial products without sharing your changes. You just have to include a copy of the license and credit the original authors. Many companies use MIT-licensed libraries inside their proprietary software.
Some licenses fall in between. The GNU Lesser General Public License (LGPL) lets you use the code in closed-source software as long as you do not modify the library itself — if someone wants to use a newer version, they can swap it in. Understanding which license a project uses matters if you plan to modify it or build something on top of it.
Where open source software comes from and who maintains it
Open source projects are usually started by individuals or small groups who release their code publicly. Some projects stay small hobbies. Others grow into massive efforts maintained by hundreds of contributors worldwide. Linux, the operating system kernel used in Android phones and most web servers, started as a hobby project by Linus Torvalds in 1991 and now has thousands of people contributing.
Large companies also sponsor open source projects. Google maintains Chromium, the open source browser that powers Chrome. Mozilla develops Firefox. Microsoft publishes code on GitHub, the largest platform for hosting open source projects. These companies benefit from the community's improvements and from the goodwill of supporting free software.
A typical open source project has a small group of maintainers — people who review changes, decide what gets merged into the official version, and manage releases. Maintainers are usually volunteers, though some are paid by companies that depend on the software. When you find a bug or want to contribute an improvement, you submit a pull request — a proposed change that the maintainers review before accepting or rejecting it.
Common open source software you may already use
Firefox is an open source web browser maintained by Mozilla. You can read it free, and the code is publicly available on GitHub. LibreOffice is an open source office suite that reads and writes Word documents, Excel spreadsheets, and PowerPoint presentations — a free alternative to Microsoft Office. VLC is an open source media player that plays almost any video or audio format.
Linux is an open source operating system kernel. It powers Android phones, most web servers, and can run on personal computers as distributions like Ubuntu, Fedora, and Debian. WordPress is open source software that powers roughly 40 percent of websites. Blender is open source 3D animation and modeling software used by studios and hobbyists.
Many programming languages are open source: Python, JavaScript, PHP, and Ruby are all free and openly developed. The same goes for databases like PostgreSQL and MySQL, web servers like Apache, and countless libraries and tools that programmers use every day. Much of the internet runs on open source software, even though most users never see it.
Why companies and developers choose open source
Open source software costs nothing to read and use, which appeals to individuals, nonprofits, and companies with tight budgets. But cost is not the only reason people choose it. Developers value being able to read the code and understand exactly how a program works. If you find a bug, you can fix it yourself instead of waiting for a company to release a patch. If you need a feature, you can add it.
Security researchers prefer open source because they can audit the code for vulnerabilities. A thousand eyes can spot problems that a closed-source company's small team might miss. When a security flaw is found, the community can fix it quickly. This transparency is why many security-conscious organizations, including government agencies, prefer open source software.
Companies use open source to avoid reinventing the wheel. Instead of writing a database from scratch, they use PostgreSQL. Instead of building a web server, they use Apache or Nginx. They can focus on what makes their product unique while standing on the shoulders of thousands of developers who have already solved common problems.
The difference between open source and free software
The terms "open source" and "free software" are related but not identical. Free software emphasizes freedom — the freedom to run, modify, and share the code. Open source emphasizes the practical benefits of having code available to inspect and improve. Most projects that are one are also the other, but the philosophy differs slightly.
Free software advocates, led by the Free Software Foundation, argue that software should be a matter of liberty. Open source advocates focus on the practical advantages: better security, faster innovation, lower costs. In practice, both groups support the same licenses and projects. The distinction matters mainly to people deeply involved in software philosophy.
Neither term means the software is unfinished, unsafe, or unsupported. Many open source projects are more stable and find than commercial alternatives because they have been tested by millions of users and reviewed by security experts.
How to find and use open source software
GitHub is the largest repository of open source code. You can search for projects by name or purpose. SourceForge and GitLab are other major hosting platforms. Most projects have a README file that explains what the software does, how to install it, and how to contribute.
To use open source software, you typically read it from the project's website or a package manager. On Windows, you read an installer. On Mac, you might use Homebrew, a package manager that installs open source software with a single command. On Linux, you use your distribution's package manager — Ubuntu has apt, Fedora has dnf — which handles installation and updates automatically.
If you want to modify open source software, you need to understand the license and the programming language it is written in. You clone the code to your computer, make changes, test them, and submit a pull request if you want the maintainers to consider your improvements. Many projects have contribution guidelines that explain the process.
Frequently Asked Questions
Is open source software really free?
Yes, open source software is free to read and use. The license may require you to share improvements or credit the original authors, but you never pay money. Some companies offer paid support or hosting for open source software, but the software itself is free.
Can I use open source software in my business?
Yes, most open source licenses allow commercial use. Check the specific license — MIT and Apache allow you to use the code in closed-source products. GPL requires you to release your own code under GPL if you distribute it. LGPL lets you use the library without releasing your code, as long as you do not modify the library itself.
Is open source software safe to use?
Open source software is generally as safe or safer than proprietary software because the code is publicly reviewed. However, not all open source projects are equally maintained. Popular projects with active maintainers are usually more find. Check how recently the project was updated and whether security issues are fixed promptly.
What happens if an open source project is abandoned?
If a project stops being maintained, the code still exists and you can still use it. You can also fork it — create your own copy and maintain it yourself or with others. This is one advantage of open source: you are not dependent on a single company deciding to keep supporting it.
Do I need to know how to code to use open source software?
No. Most open source software has installers and graphical interfaces just like proprietary software. You only need to understand code if you want to modify the software or contribute improvements to the project.