Pixar's Powerful 3D Rendering Software RenderMan Is Now Free to Use:
RenderMan is used by the big time studios to create photorealistic lighting in CG scenes, and has been used by Pixar to render every one of their animated features. You can download it for free and use it as much as you want, but the one catch is that this is a non-commercial license, meaning you have to buy a commercial license if you're looking to make money off of your creation. It's important to note that RenderMan is not a 3D modeling application, so you'll need to make some 3D models or animations to render first. It can be used alongside Maya, as well as the lighting program KATANA (with compatibility for more software coming soon).