Cocos simplifies game creation and distribution with Cocos Creator
Free, cross-platform 2D game engine powered by Haxe and OpenFL
Source of Mana is a unique 2D MMORPG
Open source library for creative expression on the web, desktop, etc.
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Your collection, your way
The Atomic Game Engine is a multi-platform 2D and 3D engine
Open-source, cross-platform, C++ game engine for creating 2D/3D games
Modern AS3 Game Engine
PixelLight is a cross-platform application framework
Modified Pokemon games for emulators or devices.