How to promote with a Open Source Licensing?

  • So i apologies for the titles misleading name, wasn't sure as to what i should title it. Anyways, i'm using Qt software/framework through the Open Source licensing (Free Edition). However, as i'm learning, i plan to promote a GUI application. I hope to get donations and perhaps at one point offer it for a small price, EX. $5. Now for this scenario, is it possible if i perhaps offer the software through the Free Edition for a small cost. The purpose of the cost would be to finance the cost for the commercial licensing Qt offers. I'm a college student, trying to stay away from law suits, etc. I don't have the financial means to protect myself in case situations occur. What do you guys think i should do?

    Also if i have a software offered free under the Open Source Licensing, must i by law offer the source code? I have a few free creations to create, but i dont want to offer the source code since i might include a Purchase Option (Like a trial etc.)!!

  • Moderators

    I can see you do not understand what Free means in Free Software. That word there is about the freedom of the users of your software. This is not about cost at all. You can sell your software without any legal problems, and you are not required to restrict yourself to "small price".

    I'll try explaining the details in a simple manner, although it is not so easy.

    In general, you have 2 options: GPL or LGPL license for Qt.

    If you choose GPL:

    • your application needs to be GPL, too
    • you can sell your product
    • you can use static linking of Qt into your application
    • you have to distribute the source code to your clients on request (and they can distribute it, too)
    • you do not need to publish the source code to everybody - you can if you want to, but it is not a requirement

    If you choose LGPL:

    • you can choose any license for your own source code (that is, your application can even have a commercial license)
    • you can sell your product
    • you cannot use static linking of Qt into your application
    • you need to inform your clients that Qt is being used (in readme, some about box, etc.), provide it's license and allow them to swap the libraries for their own
    • you do not need to give your source code to anybody (depends on which license you choose for your own sources)

    Of course, there are many more details to this, and the lawyers always have the final word here, but it should give you a base to refer to.

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