Answers.Body: <p>GPL-licensed software cannot become closed software. If you 'fork' it, then the rights on this fork remain the same (see <a href="https://en.wikipedia.org/wiki/GNU_General_Public_License" rel="nofollow">GNU General Public License</a> on Wikipedia).</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T12:49:46.840Z
Answers.Text: Why downvote? It's correct.
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T20:49:34.540Z
Answers.Text: So, there is so exception for chess engines right? It is the same?
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T21:15:14.463Z
Answers.Text: No exception* sorry for typo
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T08:42:26.593Z
Answers.Text: It is all the same. When GPL was created I do not think that they thought about chess :-) The license is only about changing and including the software. If you 'call' for example stockfish from another application then you install stockfish executable next to the application.
Answers.UserDisplayName: Marco
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T17:11:49.747Z
Answers.Text: Why do you think that they should have thought about chess? What's the exception?
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T19:00:06.043Z
Answers.Text: There is NO exception and there is no exception needed. Once GPL, always GPL.
Answers.UserDisplayName: Marco
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T20:41:18.797Z
Answers.Text: That was what I wanted to hear :)
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T08:43:51.533Z
Answers.LastActivityDate: 2016-07-28T17:43:07.930Z
Answers.LastEditDate: 2016-07-28T17:43:07.930Z
Answers.UserDisplayName: Marco
Answers.Body: <p>Short answer: No. But for chess, <strong>the answer: Yes</strong>. Read on.</p>
  
  <p>GPL is quite complicated. Essentially, it requires the application be open-source.</p>
  
  <p>From: <a href="http://www.gnu.org/licenses/gpl-faq.html#GPLCommercially" rel="nofollow noreferrer">http://www.gnu.org/licenses/gpl-faq.html</a></p>
  
  <p><strong>Can I sell a GPL project?</strong></p>
  
  <blockquote>
    <p>You are allowed to sell copies of the modified program commercially, but only under the terms of the GNU GPL. Thus, for instance, you must
    make the source code available to the users of the program as
    described in the GPL, and they must be allowed to redistribute and
    modify it as described in the GPL.</p>
  </blockquote>
  
  <p>Thus, it's ok to sell the Stockfish chess engine which is licensed as GPL. </p>
  
  <p><strong>Why open my source?</strong></p>
  
  <blockquote>
    <p>A crucial aspect of free software is that users are free to cooperate. It is absolutely essential to permit users who wish to help
    each other to share their bug fixes and improvements with other
    users.</p>
  </blockquote>
  
  <p>In theory, whoever gets the source code could improve the engine and therefore benefit the whole community. However, in practice this has never worked well.</p>
  
  <p><strong>Can I change the license to something more restrictive?</strong></p>
  
  <blockquote>
    <p>No. The GPL says that your modified versions must carry all the
    freedoms stated in the GPL. Thus, anyone who receives a copy of your
    version from you has the right to redistribute copies (modified or
    not) of that version. You may not distribute any version of the work
    on a more restrictive basis.</p>
  </blockquote>
  
  <p>But... <a href="http://www.chessclub.com" rel="nofollow noreferrer">ICC Chess Club</a> bundles their software with the Stockfish engine and I don't have their source code. Is that illegal? No.</p>
  
  <p><strong>CHESS IS DIFFERENT</strong></p>
  
  <p>Chess engine almost always runs as a separate process from the application itself, connected to the application through pipes. This is very different to traditional programming where you bundles the GPL source code within the application.</p>
  
  <p>Technically, there is no need to <em>link</em> (statically or dynamically) the GPL engine while compiling the GUI application. The engine itself is an executable that can run <em>independently</em>. Everything in the FAQ is only valid if the application <strong>links</strong> with the engine, if that isn't the case, there is <strong>no such thing</strong> as GPL license restriction.</p>
  
  <p>Try to download Stockfish, do you see something like Stockfish_64bits.exe? This is a working executable that is independent to whatever chess GUI you'd like to use. You can even run it directly in the terminal. The engine is not linked to any chess GUI, thus it's always legal to bundle it with a commercial non-GPL chess GUI.</p>
  
  <p>You can read more <a href="https://softwareengineering.stackexchange.com/questions/110380/call-gpl-software-from-non-gpl-software">here</a></p>
  
  <p><strong>What does that mean?</strong></p>
  
  <p>It's perfectly legal to bundle a chess engine with a closed-source application if the engine is an independent executable. The GPL license simply don't apply here. But if you compile the engine with the application, you <strong>must</strong> provide the source code for your entire application. For example, ICC Chess Club is allowed to distribute the Stockfish engine without providing you their source code.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T12:52:48.993Z
Answers.Text: Nice effort but it's actually answer of another question. I'm asking about chess engines, not chess apps that run engines inside.
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T12:56:27.733Z
Answers.Text: @Saibot I answered like that because you were asking about chess application in another post and then notified me about your question. Please note chess engine by itself is totally useless and meaningless in all circumstance. If u insist on only and only engine then the answer is NO.
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T20:47:27.957Z
Answers.Text: Sorry but I never asked for chess apps, also the question is very clear in this topic. For some reason you want to believe that I ask about apps. I also totally disagree that "chess engine by itself is totally useless and meaningless in all circumstance" How do you think chess engines are developed, by aliens? Chess engines are usually based on another engines, for example Rybka is based on Fruit, Komodo is based on Doch, Stockfish is based on Glaurung.
Answers.UserDisplayName: ferit
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T08:43:10.410Z
Answers.Text: Do not think that there is an exception clause for chess in GPL :-)
Answers.UserDisplayName: Marco
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T08:44:15.273Z
Answers.Text: @Marco did you even read it? Nobody said about exception.
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-30T08:47:34.727Z
Answers.Text: `Chess is different` sounds like exception. The case that you describe goes for other types of software too. BTW. The question was about modifying and changing the license, your reply not.
Answers.UserDisplayName: Marco
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-12-29T08:57:23.013Z
Answers.LastActivityDate: 2015-12-29T09:03:57.730Z
Answers.LastEditDate: 2017-04-12T07:32:02.393Z
Answers.UserDisplayName: SmallChess
Body: <p>Is it legal to modify and redistribute a GPL engine, under a more restrictive license (for example closing the source code)?</p>
  
Tags: <engines>
Title: Do GPL-licensed engines permit modifying and closing the source code?
ThreadText: # Do GPL-licensed engines permit modifying and closing the source code?
  
  (Asked by: username_0 on 2015-12-29)
  
  Is it legal to modify and redistribute a GPL engine, under a more restrictive license (for example closing the source code)?
  
  **Tags:** engines
  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_1 on 2015-12-29. Score: 3 | Accepted answer
  
  GPL-licensed software cannot become closed software. If you 'fork' it, then the rights on this fork remain the same (see [GNU General Public License](https://en.wikipedia.org/wiki/GNU_General_Public_License) on Wikipedia).
  
  > **Comments:**
  > **username_0**: Why downvote? It's correct.  
  > **username_0**: So, there is so exception for chess engines right? It is the same?  
  > **username_0**: No exception* sorry for typo  
  > **username_1**: It is all the same. When GPL was created I do not think that they thought about chess :-) The license is only about changing and including the software. If you 'call' for example stockfish from another application then you install stockfish executable next to the application.  
  > **username_0**: Why do you think that they should have thought about chess? What's the exception?  
  > **username_1**: There is NO exception and there is no exception needed. Once GPL, always GPL.  
  > **username_0**: That was what I wanted to hear :)  
  
  ---
  
  ### Answer by username_2 on 2015-12-29. Score: 2
  
  Short answer: No. But for chess, **the answer: Yes**. Read on.
  
  GPL is quite complicated. Essentially, it requires the application be open-source.
  
  From: [http://www.gnu.org/licenses/gpl-faq.html](http://www.gnu.org/licenses/gpl-faq.html#GPLCommercially)
  
  **Can I sell a GPL project?**
  
  > You are allowed to sell copies of the modified program commercially, but only under the terms of the GNU GPL. Thus, for instance, you must
  > make the source code available to the users of the program as
  > described in the GPL, and they must be allowed to redistribute and
  > modify it as described in the GPL.
  
  Thus, it's ok to sell the Stockfish chess engine which is licensed as GPL.
  
  **Why open my source?**
  
  > A crucial aspect of free software is that users are free to cooperate. It is absolutely essential to permit users who wish to help
  > each other to share their bug fixes and improvements with other
  > users.
  
  In theory, whoever gets the source code could improve the engine and therefore benefit the whole community. However, in practice this has never worked well.
  
  **Can I change the license to something more restrictive?**
  
  > No. The GPL says that your modified versions must carry all the
  > freedoms stated in the GPL. Thus, anyone who receives a copy of your
  > version from you has the right to redistribute copies (modified or
  > not) of that version. You may not distribute any version of the work
  > on a more restrictive basis.
  
  But... [ICC Chess Club](http://www.chessclub.com) bundles their software with the Stockfish engine and I don't have their source code. Is that illegal? No.
  
  **CHESS IS DIFFERENT**
  
  Chess engine almost always runs as a separate process from the application itself, connected to the application through pipes. This is very different to traditional programming where you bundles the GPL source code within the application.
  
  Technically, there is no need to *link* (statically or dynamically) the GPL engine while compiling the GUI application. The engine itself is an executable that can run *independently*. Everything in the FAQ is only valid if the application **links** with the engine, if that isn't the case, there is **no such thing** as GPL license restriction.
  
  Try to download Stockfish, do you see something like Stockfish\_64bits.exe? This is a working executable that is independent to whatever chess GUI you'd like to use. You can even run it directly in the terminal. The engine is not linked to any chess GUI, thus it's always legal to bundle it with a commercial non-GPL chess GUI.
  
  You can read more [here](https://softwareengineering.stackexchange.com/questions/110380/call-gpl-software-from-non-gpl-software)
  
  **What does that mean?**
  
  It's perfectly legal to bundle a chess engine with a closed-source application if the engine is an independent executable. The GPL license simply don't apply here. But if you compile the engine with the application, you **must** provide the source code for your entire application. For example, ICC Chess Club is allowed to distribute the Stockfish engine without providing you their source code.
  
  > **Comments:**
  > **username_0**: Nice effort but it's actually answer of another question. I'm asking about chess engines, not chess apps that run engines inside.  
  > **username_2**: @Saibot I answered like that because you were asking about chess application in another post and then notified me about your question. Please note chess engine by itself is totally useless and meaningless in all circumstance. If u insist on only and only engine then the answer is NO.  
  > **username_0**: Sorry but I never asked for chess apps, also the question is very clear in this topic. For some reason you want to believe that I ask about apps. I also totally disagree that "chess engine by itself is totally useless and meaningless in all circumstance" How do you think chess engines are developed, by aliens? Chess engines are usually based on another engines, for example Rybka is based on Fruit, Komodo is based on Doch, Stockfish is based on Glaurung.  
  > **username_1**: Do not think that there is an exception clause for chess in GPL :-)  
  > **username_2**: @username_1 did you even read it? Nobody said about exception.  
  > **username_1**: `Chess is different` sounds like exception. The case that you describe goes for other types of software too. BTW. The question was about modifying and changing the license, your reply not.  
  
  ---
  
  