Do I need to buy the Qt Framework?
I want to develop a C++ application that will work on ALL operating systems. This application will be free until version 1.5 (to make sure it is of high quality). I do not want this application to be open source. The public will only have access to the installer "EXE" and that is it. All source code will be kept and maintained by me, and not under a legal company (for now at least).
So with the information above do I need to buy the Qt framework or can I use the free version? I am always confused with these free license agreements like LGPL and GPL. I can read it a million times and still not know if I can use it or not.
If I can use the Qt for free, in regular non legal terms; what must I do or how will be restricted so that I can see Qt for free.
I really hope I can use the Qt for free, for when this application does cost money I still want to have a free version, with less feature and the paid version will still be very cheap. Not enough to make me rich, just enough so I don't go broke haha. We are talking like $5 for the paid version or something.
Answer
You can (and we do) sell commercial apps based on the Qt libs.
All you need to do is.
1, Dynamically link your exe against the Qt dll's. so your product's installer includes your app.exe and only the used Qtcore4.dll etc. This is a good idea anyway because you can upgrade your app without having to change MBs of dlls.
2, If you fix or change anything in Qt you need to offer the changes (to the Qt sources only) to your customers and/or back to the Qt people. This is pretty unlikely since Qt is very high quality.
The only reason to buy a Qt license is if you need to run on a platform where dynamic linking isn't possible - perhaps a settop box - or you need extra technical support.
ps. Even if you don't modify Qt you do need to provide the original Qt source if a customer asks for it. But this is just a matter of pointing them at the Qt site.
There is never any requirement to reveal your source code.