Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Construct 2 - Scirra Construct is a 2D game development engine with a focus on building games visually.
BYOND - BYOND is the premier community for making and playing online multiplayer games.
PlayCanvas - PlayCanvas is an open-source game engine built on WebGL and WebVR.