Public-domain software

Public-domain software is software that has been placed in the public domain: in other words, 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 software licenses grant limited usage rights.

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 Berne Convention also covers programs. Therefore, a program is automatically subject to a copyright, and if it is to be placed in the public domain, the author must explicitly disclaim the copyright and other rights on it in some way, e.g. by a waiver statement. In some Jurisdictions, some rights (in particular moral rights) cannot be disclaimed: for instance, civil law tradition-based German law's "Urheberrecht" differs here from the Anglo-Saxon common law tradition's "copyright" concept.

In the 1950s to the 1990s software culture, as original academic phenomena, "public-domain" (usually abbreviated to "PD") software was popular. This kind of freely distributed and shared "free software" combined the nowadays differentiated software classes of freeware, shareware and free and open-source software and was created in academia, and by hobbyists and hackers. As software was often written in an interpreted language such as BASIC, the source code was needed and therefore distributed to run the software. PD software was also shared and distributed as printed source code (type-in program) in computer magazines (like Creative Computing, SoftSide, Compute!, Byte etc.) and books, like the bestseller BASIC Computer Games. Early on, closed-source software was uncommon until the mid-1970s to the 1980s.

...
Wikipedia