Project address: GTK+
GTK+ is one of many GUI libraries based on C with support for C++.
Native look is emulated using theming (GTK2) or CSS (GTK3). Does not look like other applications from the same platform on platforms different than Linux.
- gtkmm - C++ bindings
- GTK+: Gnome cross platform GUI API programming Tips and Tricks - yolinux.com
- GTK+ tutorial - zetcode.com