Panda3D is a game engine, a framework for 3D rendering and game development for Python and C++ programs. Panda3D is Open Source and free for any purpose, including commercial ventures, thanks to its liberal license. Go ahead and grab it here. To learn more about Panda3D's capabilities, visit the gallery and the feature list. To learn how to use Panda3D, check the documentation resources. If you get stuck, ask for help on the forums, our community is very active.
The engine uses the very readable Python language for scripting a complete game engine. Not just a rendering engine like others, but tools for just about everything you need to make a game.
The best part is the community. There's a forum ready to answer your questions or even creating tools like the new Blender exporter for 2.5+.
The only thing stopping me from giving it a 10/10 is a scene editor, although there are attempts made by the community (see?) so you can either wait to see an official editor one day or make one yourself.