Godot Engine - Feature-packed 2D and 3D open source game engine.
wxWidgets - wxWidgets: Cross-Platform GUI Library
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
Electron - Build cross platform desktop apps with web technologies
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.