Public-domain software

Public-domain software is software that has been placed in the public domain, in other words, software for which there is absolutely no ownership such as copyright, trademark, or patent. Software in the public domain can be modified, distributed, or sold even without any attribution by anyone; this is unlike the common case of software under exclusive copyright, where licenses grant limited usage rights. As result, public-domain software has all the four freedoms of free software but is not hampered by the complexities of attribution (restriction of permissive licensed software) or license compatibility (issue with copyleft licensed software).

Under the Berne Convention, which most countries have signed, an author automatically obtains the exclusive copyright to anything they have written, and local law may similarly grant copyright, patent, or trademark rights by default. The Convention also covers programs, and they are therefore automatically subject to copyright. Thus, to release a work into the public domain, the author must take explicit action to give up these exclusive rights; procedures and limitations on this process vary by jurisdiction.