PICO-8 - Lua-based fantasy console for making and playing tiny, computer games and programs.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Photon - The fastest way to build beautiful Electron apps using simple HTML and CSS.
Unity - The multiplatform game creation tools for everyone.
Beamable - Beamable provides an SDK that enables game makers to easily add social, commerce and content management features to their games with drag-and-drop prefabs inside Unity.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.