Open source HTML5 game framework that offers WebGL and Canvas
Desktop/Android/HTML5/iOS Java game development framework
A simple and easy-to-use library to enjoy videogames programming
Open source library for creative expression on the web, desktop, etc.
Examples of procedural geometry for Unity3D C#
Open-source, cross-platform, C++ game engine for creating 2D/3D games
Hungry Hero is an open source Flash game built on Starling Framework.