Which type of software is created and updated by a worldwide community of programmers and is available for free?

Open source is created and updated by a worldwide community of programmers and is available for free. Many students are in luck, as they can easily study publicly accessible codes and have a possibility to make better software. It also has lots of advantages, such as getting high-quality results when the source code is passed around, tested and fixed. The most important thing - it is a valuable learning opportunity for programmers and opportunity to improve their skills.