Godot Engine - Feature-packed 2D and 3D open source game engine.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Babylon.js - A complete JavaScript framework for building 3D games with HTML5, WebGL and Web Audio
Corona SDK - Cross-platform mobile app development.