Tombstone Engine - A direct successor to the C4 engine.
Babylon.js - A complete JavaScript framework for building 3D games with HTML5, WebGL and Web Audio
Armory3D - Armory 3D is a free and open source game development software developed using Haxe and Kha and made to run inside Blender.
PlayCanvas - PlayCanvas is an open-source game engine built on WebGL and WebVR.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
Urho3D - Urho3D is a lightweight, cross-platform rendering and game engine implemented in C++ and released...