HaxeFlixel - Create cross-platform games easier and free. All with one codebase.
Unity - The multiplatform game creation tools for everyone.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
Godot Engine - Feature-packed 2D and 3D open source game engine.
HaxePunk - HaxePunk is a 2d game engine written in Haxe for cross-platform deployment.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.