Many thanks to everyone who provided feedback and encouragement. I've revised the document quite a bit, trying to incorporate your suggestions, and you can see the latest version at: http://zooko.com/license_quick_ref.html Also, I'll append the latest version to this e-mail. One question I have is that <[EMAIL PROTECTED]> suggested that I add licenses. As I mention in the document, I explicitly want to cover a *minimal* set of licenses, but if there is a license that you think really ought to be added, please let me know (and also let me know what values it should have in the table!). By the way, I've received notice that the license_quick_ref.html will be posted to newsforge.com soon, so I expect a lot more hits. Regards, Zooko ------- begin appended license_quick_ref.txt zooko.com [*]introduction | [*]current events | [*]stuff Quick Reference For Choosing a Free Software License All hyperlinks which lead to a different web site are marked with this symbol: [-->] QUICK REFERENCE FOR FREE SOFTWARE LICENSES, version 0.8.3, 2001-08-15 License | Community likes to accept code under it | | Combine with proprietary and redistribute | | | Combine with GPL and redistribute | | | | Must share source of redistributed version | | | | | Must contribute patents | | | | | | Indemnify against lawsuits | | | | | | | | | | | | | | v v v v v v v --- --- --- --- --- --- --- X11/BSD-new Y Y Y N N N GNU LGPL Y Y Y Y N N GNU GPL Y? N Y Y N N Mozilla PL 1.1 N? Y N1 Y? ? ? Common PL Y2 Y N3 Y Y Y Key: * "?" means I'm not sure. * "1" MPL 1.1 can be specifically amended to allow combining with GPL, according to the FSF's license list[-->] * "2" the "Common Public License", which was written by IBM and which serves as the template from which the IBM Public License is generated, is little-known, but liked by those who know of it; However, the community strongly dislikes having to deal with unfamiliar licenses, because they raise unexplored legal issues * "3" Modules under Common PL cannot be combined with modules under GPL, even though the FSF wishes that they could. The reason is that the Common PL forbids you from extending an open source app with some code on which you have a patent, and then redistributing the resulting new-app unless you accompany it with a patent license that allows people to use it. RMS didn't think of that when he wrote the GPL, and I predict that the FSF will add something like it in a future version of the GPL, but in the meantime there is the ironic situation that since the Common PL is more restrictive than the GPL license, it is illegal to redistribute an app made up of combined GPL and Common PL code. By the way, since a lot of extant free software is licensed under "Version 2 of the GPL or any later version"[-->], if the FSF were to come up with a new version of the GPL which allowed linking with Common PL'ed code, then you could immediately combine your Common PL'ed and GPL'ed code together and ship the resulting app as soon as you heard the news. Or even before you heard the news, as long as the new version of the GPL was already in existence at that time. Weird, eh? Explanations of columns: * "Community likes to accept code under it" -- I intend this to mean whether members of the community like to use source code under this license, instead of whether members of the community like to create new source code under this license. This is because I'm assuming that the reader has already created their own source code, and I'm assuming that they want their source code to be used as widely possible by members of the open source/free software community. The difference between these two meanings of "likes it" is shown up by the case of the GPL: a hypothetical open source/free software hacker may prefer to create source code under the GPL, but may prefer to use source code licensed to her under a license that permits her to combine the licensed source code with proprietary source code. This is obviously subjective (maybe the community doesn't really like The Frobozz Public License, but my biased perspective makes me think that they do), but it is a very important factor when deciding what license to use. If you feel that my summary above is inaccurate, please let me know. * "Combine with proprietary and redistribute" -- Is it legal to accept code from its author under the terms of this license, combine it with proprietary code, and ship the resulting application to a third person without giving them freely licensed source code of the proprietary part? * "Combine with GPL and redistribute" -- It is legal to accept code from its author under the terms of this license, combine it with GPL'ed code, and ship the resulting application to a third person? * "Combine with MPL and redistribute" -- It is legal to accept code from its author under the terms of this license, combine it with MPL'ed code, and ship the resulting application to a third person? * "Must share source of proprietary version" -- Does this license forbid the recipient of the source code from modifying it and shipping his modified version to a third party without giving them the source? * "Must contribute patents" -- Does this license require that if the recipient combines the code with his own contribution and then ships the resulting combined app, that he must contribute a license to any patents that he holds that would restrict usage of the resulting app. * "Indemnify against lawsuits" -- Does this license protect the original author from damages that might result from a lawsuit incurred by the use that the recipient puts the code to? Disclaimers This Is Not Legal Advice I am not a lawyer, and this is not legal advice. I do not accept any responsibility or liability for the consequences of any actions you may take after reading this document. (Note: some lawyers have already written to me to suggest that this document looks like legal advice, and that this could get me into trouble. While I sincerely appreciate their help, I am unsure how to proceed. Apparently the only way to be safe against the accusation of having given "legal advice" is to write with such ambiguity and obfuscation that nobody can learn anything from what you've written. Presumably this culture of fear increases the demand for lawyers' services. I value speaking plainly, and I feel that plain discussion of software licenses is much needed. In particular, this document would be useless if it all specifics were removed in favor of cautious generalities. Therefore, I simply reiterate that I am not a lawyer and that I am not acting as one in describing my understanding of the law in simple terms.) Bugs There are probably incorrect statements in this document -- I have already discovered several such "bugs" from earlier versions. If you see one, please inform me so that I can fix it. My goal in writing this document is to provide information for people who are choosing a free software license for their own projects. My goal in this document is not advocacy. Bias Nonetheless, my biases will inevitably show through in places. One prominent example of my bias is that I arranged it so that the answer is "Y" for all the features that I personally like. For example, in the case of "Must share source of redistributed version", I could have called it "Can redistribute proprietary version", and NOT'ed all the values, but I wanted to be able to scan across a row counting "Y"'s as good and "N"'s as bad. If you think that allowing recipients of your code to alter the code and ship proprietary versions is good, then I suggest you make a copy of the table, remove the "Not" from that column heading, and NOT all the values in that column. Then it will be easier for you to read with value-judging eyes. (By the way, it would be cool if someone would write a CGI script which asks you to enter your own preference and then shows you this quick reference card with the right settings.) An even more insidious example of my bias is what I've omitted. I tried to pick only the licenses which free software/open source hackers might seriously be considering using. The Sun Community Source License and the Microsoft Shared Source License, for example, do not appear.[footnote 1] Moreover, I have deliberately tried to omit licenses which are "overshadowed" by another license which has substantially similar characteristics but is more widely known and used. The goal of this document is to help people choose a license for their own code, not to provide a map of all extant licenses, and I assume that authors prefer a widely known and used license over an equivalent but obscure one, or (gack!) inventing Yet Another Free Software License of their own. Issues What About Public Domain? According to these messages on the opensource.org license-discuss mailing list: [1[-->], 2[-->], 3[-->], 4[-->], 5[-->]], it is not clear that it is even possible to voluntarily place your software into the public domain under United States law. There is a common myth that one can do so simply by creating a work and writing "This software/work/text is hereby placed in the public domain.", but that does not do, legally, what it is commonly believed to do. For example, it might later be possible for you to assert your ownership over the code and forbid others to use it. Also, it might be possible for a user to sue you as the author of the code. If you want your source code to be usable in that way, then you should consider using the X11 or modified BSD license, which add only the restrictions that the copyright notice and disclaimer of warranty remain intact. The License Does Not Restrict The Copyright Holder! The most common misunderstanding about software licenses is that giving someone else a copy of your source code under a license restricts what you are allowed to do with your source code. The truth is, if you write some code, and give it to someone else under the terms of License X, or publish it so that anyone may use it under the terms of License X, that this does not subject you to the terms of License X! You are the author of the code, and you hold the copyright, and giving someone permission to use the code does not restrict you to using the code in only the way that they are allowed to use it! Now it may be that some licenses do contain clauses which constrain the original author. I'm not sure whether any of the five licenses in our quick reference contain any such clauses, nor, if they, do whether they are legally enforceable. But the important myth that I wish to dispel is the notion that giving someone permission to use your source code automatically restricts how you may use your source code. For example, if I give you permission to make copies of a document that I have written, but only if you stand on your head while doing so, this does not mean that I must stand on my head whenever I make copies of my document. But What About Patches? However, there is a catch. Suppose you publish your code under License X, and then another person writes a patch that fixes bugs and adds features, and sends you the patch, and you add the patch to your own source tree and publish a new version. Now, what rights do you have to the contents of the patch? And how did including the patch into your source code affect your rights to the source code? This is a murky area. People who have thought about it seem to be of the opinion that if the patch is sufficiently small and simple, then it has no legal effect, but that if it is a large and complex patch, that you need permission from the author of the patch (who is, naturally, the holder of the copyright to the patch) before you can "combine" the patch with your source code and ship the resulting "derived work". But suppose that you and the author of the patch didn't discuss the matter? Now it gets really murky. It might be the case that the author of the patch could later sue you for having used his patch in a way that he didn't want, but on the other hand a court might rule that by sending the patch to you, it was understood that he was giving you the right to use it. Most actual hackers seem to assume that submitters of patches are automatically granting the recipient a license to use the patch and to use the combined work derived from combining the patch with the original source tree. As far as I know, this assumption is not supported by any legal fact. This appears to be an open issue to me and I hope that the community, especially the legally trained members of the community, will speak up. Explanations of rows: Please use the FSF's list of free software licenses[-->] and opensource.org's list of open source licenses[-->] to find out more about these licenses. * "X11/BSD-new" is listed on the FSF's site as "The X11 license" and "The modified BSD license". The modified BSD license is listed on the opensource.org site as "The BSD license". The opensource.org site does not include the X11 license, but it does list "The MIT license", which is very similar to X11/BSD-new, except that X11/BSD-new forbid the recipient from using the name of the author to endorse or promote products, and the MIT license does not. * "GNU LGPL" is listed on the FSF's site as "The GNU Lesser General Public License (or GNU LGPL for short)". It is listed on the opensource.org site as "The GNU Library or 'Lesser' Public License (LGPL)". * "GNU GPL" is listed on the FSF's site as "The GNU General Public License (or GNU GPL for short)". It is listed on the opensource.org site as "The GNU General Public License (GPL)". * "Mozilla PL 1.1" is listed on the FSF's site as "The Mozilla Public License (MPL)". It is listed on the opensource.org site as "The Mozilla Public License 1.1 (MPL 1.1)". * "Common PL" is a "license template", with spaces where you can write the name of the author of the software. The IBM Public License v1.0 is what you get when you take the Common Public License v0.5 and write in "International Business Machines" in the spaces. The IBM Public License is listed on the FSF's site as "IBM Public License, Version 1.0". The IBM Public License is listed on the opensource.org site as "The IBM Public License". Neither site mentions the Common Public License itself, which you can find on IBM's developerWorks site[-->]. Other Resources An up-to-date and accurate list of free software/open source licenses[-->] is maintained by the FSF. It is a useful reference even if you do not share the FSF's values with respect to source licenses. If this document and the FSF's list disagree on a point of fact or a point of law, then it is very likely a bug in this document and I would like to know about it. opensource.org hosts a mailing list specifically about this issue. You can browse the archives[-->]. They also have a list of licenses[-->] that meet the Open Source Definition. As of this writing the list on opensource.org appears to be less up-to-date and comprehensive than the list on the FSF's site. footnote [1]: That was a joke, mentioning Microsoft's so-called "Shared Source" license. That license is in no way a free software or open source license. ------------------------------------------------------------------------ Based on "license_quick_ref.html", originally written by Zooko in 2001 and posted to "http://zooko.com/license_quick_ref.html";. written in 2001 by Zooko; You may copy and use this document in unmodified form. Alternatively, you may copy and use this document in modified form, provided that you remove this line (that begins: 'written in 2001 by Zooko...') and retain the line above (that begins: 'Based on "license_quick_ref.html"...'). Zooko O'Whielacronx Last modified: Wed Aug 15 07:18:50 PDT 2001
