Torque2D
A completely free, open-source, 2D game engine
...The engine includes essential components such as a batched OpenGL renderer, Box2D physics integration, OpenAL audio support, automated asset management, and sprite and skeletal animation systems that simplify bringing characters and environments to life. With a modular project structure and support for object persistence using TAML, developers can build complex games with reusable systems and clear project organization. Torque2D also includes its own scripting language, enabling rapid iteration and gameplay scripting without deep engine modification.