Editing NetHack (section)

===Licensing, ports, and derivative ports===
{{Infobox software license
| name = NetHack General Public License (NGPL)
| image = 
| caption = 
| author = Mike Stephenson et al.
| version = 
| date = 1989
| OSI approved = Yes
| Debian approved = 
| FSF approved = 
| GPL compatible = 
| copyleft = Yes
| linking = 
| website = https://www.nethack.org/common/license.html
}}
''NetHack'' is released under the NetHack General Public License, which was written in 1989 by Mike Stephenson, patterned after the [[GNU bison]] license (which was written by [[Richard Stallman]] in 1988).<ref>GNU Bison is no longer distributed under the original Bison license; it has been distributed under an extension of the [[GNU General Public License]] since at least 1991.[http://dinosaur.compilertools.net/bison/bison_3.html]</ref> Like the Bison license, and Stallman's later [[GNU General Public License]], the ''NetHack'' license was written to allow the free sharing and modification of the [[source code]] under its protection. At the same time, the license explicitly states that the source code is not covered by any [[warranty]], thus protecting the original authors from [[litigation]]. The NetHack General Public License is a [[copyleft]] [[software license]] certified as an [[open source license]] by the [[Open Source Initiative]].<ref>{{cite web|url=https://opensource.org/licenses/alphabetical|title=Licenses by Name|website=Open Source Initiative|access-date=16 December 2015}}</ref><ref>{{Cite web |url=https://opensource.org/licenses/NGPL |access-date=2016-04-23 |title=The Nethack General Public License (NGPL) |publisher=opensource.org |archive-date=29 April 2016 |archive-url=https://web.archive.org/web/20160429115623/https://opensource.org/licenses/NGPL |url-status=dead }}</ref>

The NetHack General Public License allows anyone to [[Porting|port]] the game to a platform not supported by the official DevTeam, provided that they use the same license. Over the years this licensing has led to a large number of ports and internationalized versions<ref>{{Cite web|url=https://nethackwiki.com/wiki/NetHack_in_other_languages|title=NetHack in other languages - NetHack Wiki|website=nethackwiki.com}}</ref> in German, Japanese, and Spanish.<ref name=":0" /> The license also allows for software forks as long as they are distributed under the same license, except that the creator of a derivative work is allowed to offer warranty protection on the new work. The derivative work is required to indicate the modifications made and the dates of changes. In addition, the source code of the derivative work must be made available, free of charge except for nominal distribution fees. This has also allowed source code forks of ''NetHack'' including ''[[Slash'EM]]'',<ref>{{Cite web|url=http://slashem.sourceforge.net/|title=The Slash'EM Homepage|website=slashem.sourceforge.net}}</ref> ''UnNetHack'',<ref>{{Cite web|url=https://github.com/UnNetHack/UnNetHack |title=UnNetHack|website=[[GitHub]]|date=21 October 2021}}</ref> and ''dNethack''.<ref>{{Cite web|url=https://github.com/Chris-plus-alphanumericgibberish/dNAO |title=dNethack|website=[[GitHub]]|date=21 October 2021}}</ref>