The Free Edition is the Qt library for UNIX/X11 for development of free software. It includes the complete source code.
You may use it free of charge as long as you adhere to the Qt Free Software License. This basically says that you must make your source code available to the users of your software, and you must give them the rights to change and redistribute your code.
Yes. You only need the Professional Edition for developing software, not for running it.
This would create problems both for commercial and free software users of Qt:
With Qt's licensing scheme, we try to make the best for both worlds: You can use it free of charge if you want to develop free software, or you can purchase the Professional Edition to make commercial or proprietary software. With a GPL'ed library, the only thing you are allowed to develop is GPL'able software. In this way, Qt gives you a freedom which a GPL'ed library does not.
The LGPL is designed to "permit developers of non-free programs to use free libraries" (quote from the LGPL). In other words, if Qt were LGPL'd, companies would not have to buy the Professional Edition in order to make commercial (non-free) software, they could just use the Free Edition, free of charge. That would mean Troll Tech would not get the revenue necessary for improving and extending Qt.
Also, item #1 under the question Why is Qt not distributed under the GNU Public License (GPL)? above applies to the LGPL also.
The reasons for why we for Qt Free Edition have our own Qt Free Software License instead of using GPL or LGPL are explained in the two previous questions: Item #1 under the question Why is Qt not distributed under the GNU Public License (GPL)? above applies even in a situation with double licensing; and for LGPL, the situation is the same.
Item #1 under the question Why is Qt not distributed under the GNU Public License (GPL)? above applies to this question also.
Other important reasons:
Yes, it is really free. No, there are no special Troll Tech license restrictions on free software produced using the Free Edition. In fact, the opposite is true: The Qt Free Software License demands that the software must be free. The users must have the rights to obtain the source code, change it, and redistribute it. It is only Qt itself that may not be changed.
We will not discontinue our strategy of releasing Qt free of charge for development of free software.
If you do not take our word for it, think a moment about what would happen if we were to do this: Our reputation among thousands of developers world wide would be irreparably damaged in an instant. People would start building Qt clones. Our business would be seriously hurt. In short, we are not at all considering doing this.
If you are still worried, consider this: Hypothetically, if this were to happen, the Qt Free Software License guarantees that the last free version of Qt could be used indefinitely free of charge, for running and developing free software. Furthermore, the free software community would be able to fix bugs and continue development of this library: using C++ inheritance, workarounds, encapsulation, alternative widgets etc., the license's requirement of not changing Qt source code can be honoured. Many existing Qt free software applications do this already; see KDE, for example. It is our experience that this can be an effective strategy; for the large majority of the bugs that have been reported for various version of Qt, we have been able to suggest satisfactory workarounds.
Typically, no. If you want to use the free license within an organization, your software must be usable outside your organization (if anyone should want to use it), you must notify Troll Tech before starting to use it, you have to allow free distribution and you have to make your source code available. (Naturally, if you purchase the Professional Edition, these restrictions do not apply.)
It is our policy that when you are using Qt for free, you should in return contribute to the free software community.
Yes. Some Linux distributions already contain Qt. Anyone can redistribute the free edition of Qt, for free or for pay, as long as they include the whole archive.
Really yes. It is a parallel situation to that of Motif, for example. Motif is non-free software, still there exists many GPL'ed applications using it.
The Free Edition is not available on Windows. You have two options:
Among our main reasons for this policy are:
We believe that our solution is better for everybody in the long run.
Yes and yes.
No. We used to offer one, but there was far too low demand to justify the administration related to it.
Are you sure? Using C++ inheritance is very often a better alternative. If you do change Qt, you may not distribute the modified toolkit or programs using it (as long as you're using the Free Edition).
We encourage you to send patches to firstname.lastname@example.org. We will try to evaluate the patches and reply as soon as they come in. If we like what we see, we'll incorporate it in the next Qt release.
There are many good reasons why we do not permit distribution of modified versions of the Qt library:
Please note that experience shows that both the latter two points apply even if the re-distribution were to contain some "README" file that explained that this were a non-Troll Tech, modified distribution.
We believe both users and developers of Qt-based applications are better served with our policy in the long run.
This is absurd. If anyone thinks there's a lot of money in this, he/she can just go ahead and do it him/herself.
But remember, most of the software is GPL'ed, so anyone could buy the windows version once and start selling/distributing it themselves. And the software could be sold statically linked, so this would not generate any additional Qt license sales for us either.
In short, we have no such plans. Those speculations seem to be made to spread FUD (Fear, Uncertainty, and Doubt).
In several ways. Pick and choose.
If the library is small, a widget or two, perhaps the best way is to submit it as a contribution. We will include your software on our list of Free Software Using Qt.
If it's larger, you can distribute it, and you can include Qt along with it. But you cannot include Qt as part of your library (e.g. by making a shared library which includes Qt and your library). Your distribution must contain the file README.QT. Your users will be Qt users as well, and Qt's licensing applies.
This applies to wrapper libraries as well, of course. If you write Ada or Perl bindings, fine. But anyone who uses your bindings will be using Qt as well, and Qt's licensing applies.