http://sandboxgamemaker.com/This tool looks really cool. It explores a variety of functions that make it easy to create a 3D game [or machinima]. According to the website, all editing is done in-game using a variety of methods.
But don't take my word for it!If you don't like reading, and prefer a video, here is one quite conveniently:
http://www.youtube.com/watch?v=g44Ww2bg2_EDoes anybody use it? If so, what do you think of it? Namely, is it worthwhile?