The free license for Qt is the LGPL, which, although more restrictive than a fully permissive license like BSD or MIT, is still suitable for many commercial app

The free license for Qt is the LGPL, which, although more restrictive than a fully permissive license like BSD or MIT, is still suitable for many commercial applications. (You can't ship proprietary modifications to Qt, but you can ship a proprietary app that includes Qt as a dependency. Your app can use a modified version of Qt if you open source your modifications.)