GTK 3.99
The part of GTK+ I've always hated the most is how much it relies on GObject, which is probably one of the worst ideas ever conceived by mankind. Reinventing a whole object system using C and shitload of macros is such an aberrant idea I cannot even start ranting on why it's an utter abomination. The fact it was born mostly from the hate the GNU project always harboured for C++ is what has always bewildered me the most. I understand that C++ in the nineties was a steaming pile of manure, but basically reinventing a poor man's copy of Objective-C just because they desperately wanted to write their stuff in C, and nothing else, is just too much.And for what? GCC was basically the reference implementation of an Objective C compiler, a language that basically boils down to an object system hastily glued on top of C. I don't think it would have been so unreasonable to use that instead of rolling their own... I guess they had their reasons for not doing that, or not cooperating with GNUstep for that matters.The irony is that has led to the creation of a million language bindings, such as Vala, Gtk#, PyGTK, Gtkmm, gjs, ... just to lower the massive learning curve of writing GTK applications in C. This is something Qt has clearly never struggled with, given that I've yet to see a relevant Qt app not based on C++ or (recently) QtQuick.