Yeah, objc is. However mentally I counted that towards the OS languages and C family languages. Swift also belongs to the OS (first class langauge) category, although it's certainly not in the C family.
For others maybe Delphi was succesful in the GUI domain. But in the last years it was certainly not often mentioned. For GTK there's also Vala, which was probably even designed to be used for GUIs.
Oh yes, it's very much a an "os language". But an important one to include in your list, I felt!
Objc is certainly C-derived, but it's also just as much smalltalk-derived. Definitely a very different beast than plain C (more so even than C++, I would say).
For others maybe Delphi was succesful in the GUI domain. But in the last years it was certainly not often mentioned. For GTK there's also Vala, which was probably even designed to be used for GUIs.