Editing Open-source license (section)

==Public domain software==
{{main|Public-domain software}}
[[File:Spacewar!-PDP-1-20070512.jpg|thumb|alt=Spaceships and stars on a round monitor| Early computer programs like the pioneering video game [[Spacewar!]] are in the public domain.{{sfn|Ross|2021|loc="Spacewar: End of Development"}}]]

When a copyright expires, the work enters the [[public domain]], and is freely available to anyone.{{sfn|Rosen|2005|p=36}} Some creative works are not covered by copyright and enter directly into the public domain. In the early history of computing, this applied to software.{{sfn|Oman|2018|pp=641-642}} Early computer software was often given away with hardware.{{sfn|Walden|2022|p=3}} Developed initially at MIT, the pioneering video game [[Spacewar!]] was used to market and test the [[PDP-1]] computer.{{sfn|Smith|2019|pp=55-56}} 

According to attorney [[Lawrence Rosen (attorney)|Lawrence Rosen]], copyright laws were not written with the expectation that creators would place their work into the public domain. Thus intellectual property laws lack clear paths to [[waive]] a copyright. Highly permissive licenses described as "public domain" may legally function as unilateral [[contracts]] that offer something but impose no terms.{{sfn|Rosen|2005|pp=74-77}}{{sfn|St. Laurent|2004|p=98}}

A [[public-domain-equivalent license]], like the [[Creative Commons]] CC0, provides a waiver of copyright claims into the public domain along with a [[permissive software license]] as a fallback. In jurisdictions that do not accept a public domain waiver, the permissive license takes effect.{{sfn|Fagundes|Perzanowski|2020|p=524}} Public domain waivers share limitations with simple academic licenses. This creates the possibility that an outside party could attempt to control a public domain work via patent or trademark law.{{sfn|Joy|2022|pp=1008-1010}} Public domain waivers handle warranties differently from any type of license. Even very permissive ones, like the MIT license, [[disclaim]] warranty and liability. Anyone using the free software must accept this disclaimer as a condition. Because public domain content is available to everyone, the copyright waiver cannot impose a disclaimer.{{sfn|Rosen|2005|p=36}}