I am really confused about software linceses, I've read a lot of articles but I can't find an answer to my question, which is: Can I develop and sell applications that uses libraries under gpl license? Like for instance, I want to use agsXMPP library in a windows phone app, and sell it in the market, so is it legal?

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    Just read the text: ag-software.net/agsxmpp-sdk/license I'm not able to give you legal advice, however: Yes you can develop and sell an application that uses libraries under gpl, as long as you provide the sourcecode for your program under GPL as well. – iveqy Nov 20 '13 at 17:18
  • Well I did understand that part, but when it comes to windows phone market, there is only where you can publish the XAP file, not like sourceforge. So how can I publish the source code? – Ayoub.A Nov 20 '13 at 17:25
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    what part of using windows phone market prevents you from using sourceforge, github, or whatever other place to release your code? – iveqy Nov 20 '13 at 17:27
  • You don't have to "publish" the source code. You have to provide the source code upon request. Most people find it easier to publish to a public site rather than deal with incoming requests piecemeal. – Steven Burnap Nov 20 '13 at 19:52

Stop reading articles, and read the actual GPL itself. It's not that hard.

Yes, you can sell applications. But if someone who receives an application asks for it, then you have to give them all the source code for anything that includes code licenced under the GPL.

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    You also need to tell the user that the software is GPL licensed. – Christian Nov 20 '13 at 18:46
  • Oh, and: you can't prevent the person you sold it to from simply giving it away. So you better make sure that your first sale pays for your work ;-) – Joachim Sauer Nov 21 '13 at 9:15

Your question is easily answered. Just read the FSF FAQ on the GPL. I linked to the FAQ that directly answers your question.

Does the GPL allow me to sell copies of the program for money?

Yes, the GPL allows everyone to do this. The right to sell copies is part of the definition of free software. Except in one special situation, there is no limit on what price you can charge. (The one exception is the required written offer to provide source code that must accompany binary-only release.)

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