Linux

As someone who is trying to develop my own Linux destkop apps, I can tell you that the day that I switch to Qt is the day Qt provides a feature that works as well as GObject Introspection (GI) does for Gtk. GI creates a cross-platform database of objects, properties, and signals, for auto-generating language bindings, so you can customize your Gtk programs with scripting languages (Python, Lua, Vala, JavaScript, Scheme). It is a relatively simple task to bind any programming language to GObjects thanks to GI.

Qt does have a QMetaObject system which is similar, but C++ is a difficult language to bind to on most operating systems because of how native language functions are labeled in the library code -- names are "mangled", a hack to work around the miss-match between object libraries features (.so or .dll files), which do not provide the ability to "overload" functions, and C++ libraries features, which do provide this ability. The function/method overloading feature is used quite often in any C++ program. But decoding mangled names for language bindings can be very error-prone without the sort of automation that GI provides.

As it is now, really the best way to develop Qt apps is to use C++, with Python for scripting, because these languages are the most well-supported by Qt (C++ natively, Python being the most stable and well-maintained "foreign" language for Qt). And I like neither of these two language. Gtk gives you a much larger selection of scripting language choices, even though it is programmed in C, and this is thanks to how well GObject Introspection works.