The game engine for everyone
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Multi-platform Engine for Desktop, XBOX (UWP) and Mobile games
New Godot bindings for Swift
Open source library for creative expression on the web, desktop, etc.
GemRB is a portable open-source implementation of the Infinity Engine
Urho3D Game engine
2D Game Engine
Multi-threaded game engine for Android
Modern AS3 Game Engine
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3