Godot Engine - Feature-packed 2D and 3D open source game engine.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
HaxeFlixel - Create cross-platform games easier and free. All with one codebase.
RPG Maker - Make your own PC game with RPG Maker. Our easy to use tools are simple enough for a child, and powerful enough for a developer. Try it free today!
Orx - Orx - a portable open source game engine
Blacksmith 2D - Black is a highly optimized 2D framework for web, mobile games, and playable ads.