What kind of software can be modified by anyone due to being open source?

Open source software is characterized by its licensing, which allows anyone to access, modify, and distribute the source code. This model promotes collaboration and innovation, as developers can contribute improvements, fix bugs, and tailor the software to meet their specific needs. The open nature of the source code typically encourages community involvement and transparency, making it a cornerstone of many modern software development practices.

In contrast, the other options do not offer the same level of accessibility or modification rights. Shareware is generally commercial software that allows users to try it for a limited period before purchasing. Freeware is software that is available for free but does not provide source code access, thus restricting modifications. Public domain software is not copyrighted and can be freely used and distributed, but it may not always allow for modification or distribution of modified versions based on its original license conditions. Therefore, open source stands out as the category that explicitly permits modification by anyone.