Pygame - Pygame is a set of Python modules designed for writing games.
Project Anarchy - Project Anarchy is a complete end to end game engine and state-of-the-art toolset for mobile.
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
Adventure Game Studio - Adventure Game Studio provides the tools to make your own adventure, for free!