Project Anarchy - Project Anarchy is a complete end to end game engine and state-of-the-art toolset for mobile.
Pygame - Pygame is a set of Python modules designed for writing games.
Limon Engine - Limon is a multi platform 3D game engine mainly focusing on first person games.
Unigine - Unigine Engine is a proprietary cross-platform middleware, developed by Unigine Corp.
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
libtwo - All-purpose c++ app prototyping library, focused towards live graphical apps and games