Kodu Game Lab - Kodu lets kids create games on the PC and XBox via a simple visual programming language.
wxWidgets - wxWidgets: Cross-Platform GUI Library
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Electron - Build cross platform desktop apps with web technologies
Godot Engine - Feature-packed 2D and 3D open source game engine.
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.