Which category of software is protected by copyright laws but is available at no cost?

Closed-source software is proprietary and not available for free, as the source code is kept secret by the developer. Users must typically purchase a license to use closed-source software, making it incompatible with the definition of software that is available at no cost.

Shareware is software that is initially provided for free but often comes with limited features or a trial period. After this period, users are encouraged to pay for a full version. Thus, shareware does not fit the criteria of being available at no cost indefinitely, as it typically requires payment for continued use or access to full features.

Public domain software is not protected by copyright laws and can be used, modified, and distributed freely by anyone without restrictions. While it is available at no cost, it does not meet the criteria of being copyright protected, as it has no legal ownership or rights associated with it.