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The GNU General Public License (GNU GPL or just GPL) is one of the most popular open-source licenses in the free software community, and for good reason; it has remained one of the strongest copy-left copyleft licenses, requiring users to share their contributions (some might say to an insane degree).

The To use GPL has two widespread versions; version 2 (written in 1991) code, the safest and version 3 (written in 2007). No one talks about version 1 (1989). The GPL3 was meant easiest way to reconcile avoid a license compatibility, address software patents, license violations, nullifying [[wikipedia:Digital_rights_management|DRM]] by calling violation is to keep the repository for it an ineffective technological measure, and out in the big one; [[wikipedia:Tivoization|Tivoization]], which was a severe flaw they completely missed when drafting open. The lack of any release demonstrates ill will among the first two versions that allowed Tivo to make use many business users of GPL2 open source software by sharing its code while preventing unsigned firmware from being loaded who usually have "playing fair with the community" on the hardwarelower end of their priorities. The GPL3 prohibits this, which proved to have major problems when Hyperkin tried to incorporate benefit of having just the GPL3-licensed [[RetroArch]] repo in the [[Retron5]] (among other violations)open is that software itself usually has a mechanism to display the software version, and even slight knowledge of repository traversal and compiler tools should allow users to reproduce their own version.

====LGPL and AGPL====The GPL As it is not the only license that chief representative of the Free Software Foundation created; because strong copyleft licenses, the GPL2 ended up being overly restrictive in how software could work with it, many open-source libraries needed a less strict license to allow interoperability with commercial softwareGPL carries misconceptions about the expectations around its use.

This ended up being solved in two ways; * The license says nothing about having to make the linking exception found in GNU Classpathprocess of compiling builds easy, only that it has to be ''possible's GPL2 '.* The license allowed it also says nothing against commercial distribution of any kind (as is explained later for non-commercial licenses). If you had to not affect make the software source code available, you could charge some arbitrary amount for it . Doing that would still be bundled in, and the Lesser GPLleaps above having nothing to show, which is an entire license that was made to make this aspect clearer rather than be an exceptionusually what happens.

The GPL also doesn't account has two widespread versions; version 2 (written in 1991) and version 3 (written in 2007). The GPL3 was only written to reconcile issues that had come up with the GPL2 in the years after it was written, as the Free Software Foundation had a considerable amount of foresight, but not enough to imagine what would happen if a company used GPL software in a product where users could not flash their own firmware. This has become the central point of contention with [[Emulation Boxes]], where hardware designers are constantly at odds with hobbyists who want to increase the functionality of their systems. ====LGPL====The GPL2 was an adequate license for software projects that compiled all of their code into a single binary. However, if the license is used exclusively for consumera <abbr title="Collections of specific routines or functions in a single file to be used by other software instead of being run directly. You may know them on Windows as Dynamic-facing serversLink Libraries, or DLLs.">code library</abbr> that requires some intermediary application, so said app becomes bound to the terms of the Affero GPL . This is a consequence of its broad reach. The FSF's original response was made to require web app developers create a "linking exception" in GNU Classpath's GPL2 license that allowed it to be used in proprietary software without having to share the whole program's source (the lack of said exception would've made it unfeasible to use in Java software). Later on, they created a much clearer variation of this exception as a separate license called the Lesser GPL (LGPL). This means code of their app that bundles and uses an LGPL library only needs to users over keep ''the library itself'' open, not the networkcode that interfaces with it.

* It's not as strict as the GPL because it also prohibits doesn't grant trademark use.

Some ostensibly "free and open-source" software licenses include, or can be modified to include, an extra provision that's designed to prevent the software from being used for any commercial purposesof a specific nature or of any kind, e.g. the sale of software and/or hardware to turn a profit. Since this is a fairly explicit example of restricting who can use a piece of software and for what purpose, it technically '''it disqualifies the software in question from being considered FLOSS''', even if the developer still makes the source code readily available to the public.

The <blockquote>''&ldquo;"Free Software Foundation explains software" does not mean "noncommercial". On the contrary, a free program must be available for commercial use, commercial development, and commercial distribution. This policy is of fundamental importance&mdash;without this, free software could not achieve its aims. [...] We must conclude that a program licensed with such restrictions does not qualify as free software.&rdquo;''<br/>&ndash;[https://www.gnu.org/philosophy/free-sw.html#selling hereThe Free Software Foundation], as part of their "What is free software" page:</blockquote>'''Free software ''can'' be commercial'''

'''6. No Discrimination Against Fields of Endeavor''' &ldquo;The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.&rdquo;''<br/>&ndash;[https://opensource.org/osd Open Source Initiative]

That being said, some emulator developers will still see nonNon-commercial licensing as licenses have long been a desirable or even essential optionfor emulator developers, either to specifically pre-empt others from bundling their code into a payware package (even though this would also be a flagrant violation of most FLOSS licensesthe GPL3) or using it in a pre-built [[Emulation Boxes|emulation box]] without their explicit permission, or because they simply haven't considered the possibility of any more legitimate commercial use cases for their projects. Or sometimes they might just be scared do it out of caution that the original hardware owners coming after manufacturers could take them and they see to court. This is despite the non-commercial clause as an easy way fact that [[#Legality of emulation|their only grounds to say, "hey, we're not trying to profit off of this, please don't sue us"stand on is whether the underlying technology behind a console is patented]].

Whatever reason the dev gives for a non-commercial clause in the software license, it ''should'' be of no consequence to the average end user who's just running a free emulator on their PC for their own use. Some specific circumstances, such as a developer who's making a brand new commercial game for an old system and using an emulator to test it in lieu of real hardware, ''might'' be exceptions to this, but that's where it admittedly gets pretty murky from a legal standpoint.