Abandonware is computer software whose copyright is no longer defended or which is no longer being sold even by the company that made it. This could be by intentional non-enforcement by its owners due to its age or obsolescence. Sometimes this is because the corporate copyright holder went out of business without transferring ownership, leaving no one to defend the copyright. (Copyrights owned by a natural person who dies become the property of the person's estate.)
Transfer of this software is still technically unlawful in most jurisdictions (except in cases of owner dissolution) as the copyright is still in effect. Abandonware changes hands based on the presumption that the time and money that a copyright holder would have to spend enforcing the copyright is greater than any money the holder would earn selling software licenses. Often the availability of abandonware on the internet is related on the willingness of copyright holders to defend their copyrights. For example, unencumbered emulators and games for Colecovision are much markedly easier to find on the Internet than unencumbered emulators and games for Mattel Intellivision in large part because there is still a company that makes money by selling Mattel Intellivision games while no such company exists for Colecovision.
Companies do sometimes voluntarily relinquish copyright, putting it into the public domain, or even releasing it as free software; id Software is notable as an early proponent of this practice. Transfer of public domain or free software is perfectly legal, distinguishing it from abandonware. However, relinquishing copyright is uncommon because the copyright owners are unclear and because there is rarely an economic incentive to do so.
The most common abandonware is old video games, either computer games or older video game console or arcade games that are played through emulation. Many people think that various older games are more fun than newer games (hence old school gamers), in part because their designers had to concentrate on game play features other than graphics, so these games have gained a second life by being distributed through the Internet. However, sometimes this conflicts with the copyright holders, but that conflict is controversial. Atari 2600 games are commonly distributed throughout the Internet based on the presumption that no one would buy a primitive Atari game. This presumption is false as mobile phone manufacturers have bought the rights to use these games, which play quite nicely on newer programmable mobile phones. Reverse piracy has inspired abandonware.
Copyright on software does not expire within its useful lifetime. In fact it may never expire if the world's legislators continue to extend copyright.