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I want to license my game, to protect my intellectual property, but I also want to make it open-source, and sell it.

I have an engine that I'd like to open-source, but I'd like to be the only one with rights to distribute it in that form. I'd like people to be able to distribute it however they wish, if it is their modified version. I'd like games made with the engine to be able to be sold, but not re-distribute the engine, and they must credit it if they do use it.

I'm not a legal expert, and I have no experience as of yet with licensing. Which licenses will allow me to do this?

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    \$\begingroup\$ "I'd like people to be able to distribute it however they wish, if it is their modified version". What do you mean by "modified version"? If changing the name is enough, then that makes your complex license kind of... overkill. If you want the changes to be 'substantial', you need to clarify it a bit... \$\endgroup\$
    – Liosan
    Aug 24 '12 at 12:44
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You should talk to a lawyer. Check out the comparison of open source licenses available to you (Or this one). Ultimately it's up to you and your lawyer to decide which one suits you best.

EDIT

To address your additional requirements. If you don't have the money to hire a lawyer to review the available licenses and match them with your requirements, you're not going to have the money to enforce any violations of the license you choose. All you can really do is ask for what you want and trust people will follow the rules you ask of them.

I recommend you do exactly that, simply add your request to the top of each of your source files. You don't need to get fancy with legal documents. Just tell people, in your own words, how you want your code used. Can you really see yourself trying to enforce the rules anyway? Going into court to defend your open source code from misuse? I find that highly unlikely.

Would it upset you if you found out someone was using your engine source code against your wishes? Sure, but the likelihood of you ever finding that out is just about nil. Same as if you had a "professional" license attached to the source.

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    \$\begingroup\$ As you might imagine, I don't have the resources at this point to hire a lawyer... \$\endgroup\$ Aug 21 '12 at 16:03
  • \$\begingroup\$ I would imagine that. But such is the legal system. Since you don't have the funds, or a lawyer, it's up to you alone. The comparison charts I linked should be enough for you to make an informed decision. \$\endgroup\$
    – House
    Aug 21 '12 at 16:08
  • \$\begingroup\$ They did indeed point me in what I believe is the correct direction, many thanks! At this point I believe I'm leaning towards an Apache License. \$\endgroup\$ Aug 21 '12 at 16:39
  • \$\begingroup\$ I'd +1 again for the edit. Excellent point. \$\endgroup\$ Aug 22 '12 at 17:47
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Your needs sounds like you'll want more than one license. The engine and tech can be released under an Open license and the content can be released under a restrictive license.

If you want to ensure that the tech cannot be used for serious commercial competition ( if you think your tech is really that special) you can use something like the GPL or a CC-NC license.

This is what id does, for instance.

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  • \$\begingroup\$ Is GPL not an open license? \$\endgroup\$ Aug 21 '12 at 16:04
  • \$\begingroup\$ It's authors prefer the term Free, but yes. I was just clarifying that the GPL is not nearly as permissive as most other "open" licenses. \$\endgroup\$ Aug 21 '12 at 16:15
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    \$\begingroup\$ @Bloodyaugust if the user is interested in doing something serious with your code, as soon as he will read "GPL" he will move your code to the trash because the GPL is only good for project that are open and will stay open, the GPL it's not permissive. \$\endgroup\$
    – user827992
    Aug 22 '12 at 4:03
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I'm going to simplify here, and also I'm not a lawyer etc etc etc. You should actually read these licenses if you're going to use them, and talking to a lawyer doesn't help either.

I'm assuming this is code you write yourself, and you will keep the copyright for it. When you use an open source license, you irrevocably grant other people the right to distribute your work possibly with certain strings attached, but for the licenses I'm familiar with, this does not take away the rights that you already have under copyright law. (ref: https://www.gnu.org/licenses/gpl-faq.html#DeveloperViolate)

Of course, if you incorporate code from third parties, you'll have to comply with the associated licensing terms.

The licenses I'm familiar with (mainly MIT, LGPL, and GPL) also do not prevent others from selling the code. GPL makes it difficult because the GPL would obligate anyone selling it to also offer source code and the rights to modify/redistribute it (and thus undercut the seller). LGPL has a weaker version of that, and MIT is a public domain equivalent license (i.e. give everyone all rights under copyright).

If you want to prevent others from redistributing your code (and making money from it), you can release the source code with your game but not offer any license to distribute it. Jason Rohrer did this with Inside a Star-filled Sky (ref: http://insideastarfilledsky.net/). If you just want to prevent other people from making money from it, Creative Commons BY-NC is good for that.

It really depends on what your goals are in releasing the source, and exactly what you want to allow people to do.

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  • \$\begingroup\$ So let me elaborate a bit. I have an engine that I'd like to open-source, but I'd like to be the only one with rights to distribute it in that form. I'd like people to be able to distribute it however they wish, if it is their modified version. I'd like games made with the engine to be able to be sold, but not re-distribute the engine, and they must credit it if they do use it. \$\endgroup\$ Aug 22 '12 at 15:27
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I think that you are approaching this on the wrong side.

Question: what you need to license, the source code or a compiled software?

In the first scenario you probably want to stick with something like the GPL, BSD or MIT licenses, in the second case you probably just need an EULA.

You also can mix this 2 requirements but i don't think that you need to give a license for your source code in your case, the user will never see your source code; you also appear to not being interested in patents, and patents are the only way to prove that you own a particular asset of your software or you own the rights for an UI, a file format, or some other pieces of your code including the design and its own implementations.

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