Godot
OVERVIEW
Godot provides a huge set of common tools, so you can just focus on making your game without reinventing the wheel. Godot is completely free and open-source under the very permissive MIT license. No strings attached, no royalties, nothing. Your game is yours, down to the last line of engine code.
FEATURES
Code in C++ or C#. Supports OpenGL rendering. Contains a built in animation system and many other features found in high end game engines and tool suites.
LINKS
Official Site: godotengine.org
Wikipedia: Wikipedia Article