Panda3D
Disney's in-house 3D engine, built for theme-park rides and online games, which went open source and found a second life in the Python world.
The engine grew up at Disney VR Studio in the 1990s for interactive attractions, then powered the MMOs Toontown Online (2003) and Pirates of the Caribbean Online (2007). The core is C++, but it is meant to be driven from Python, with a scene graph at its heart and back ends for both OpenGL and DirectX.
Disney released the code in 2002, Carnegie Mellon's Entertainment Technology Center took on much of the upkeep, and the licence later became BSD. Panda3D never made it big commercially, but it is well liked in teaching and research — a more natural step than Pygame once you want proper 3D.