Grit Game Engine - The Grit Game Engine is an MIT-Licensed Open Source Game Engine that is highly scriptable via Lua.
Unity - The multiplatform game creation tools for everyone.
Pygame - Pygame is a set of Python modules designed for writing games.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Unigine - Unigine Engine is a proprietary cross-platform middleware, developed by Unigine Corp.