Can I build Qt projects statically for free if I don't sell or release them publicly?
I am wanting to build some projects statically using mingw with Qt GUI, these projects will not be released in any way, they are just for me and my friend to use to help us keep in touch. If I build these statically and only use the program privately am I ok or would I be breaking the license?
AFAIK, you need to use GPL for that, but yes, you should be fine. GPL license does not force you to publish the code to the whole world, it's enough for you to share it with your friend (on request).
s/friends/users of your application/.
Your friends are free to pass on copies to whomever they like, and you need to give the code to those people on request, too.
At least that is my understanding of the GPL, but I am not a lawyer. Get legal advice from a expert in your country to clear this up.