what is public domain software

Public domain software is software that is not protected by copyright laws of any nation and can be freely used, modified, distributed, or sold without any restrictions. It is different from free software, which is still copyrighted, but the authors copyright is retained and used to enforce copyleft or to hand out permissive-licensed software. Public domain software can be modified, distributed, or sold even without any attribution by anyone, unlike software under exclusive copyright, where licenses grant limited usage rights. Public domain software was popular in the software culture of the 1950s to 1990s, and it was created in academia, by hobbyists, and hackers. Public domain software is not the same as freeware or shareware, which can be obtained for free or a small fee but are still copyrighted. Examples of public domain software include SQLite, I2P, CERN httpd, and GNU.