What software? Well it depends on what you want to do. For 3D modeling kind of stuff, I only use POVRay since it's free and well thought-of. I like it a lot. Some animations I did using METAL basic. This amounted to generating a large graphic with all of the frames for the animation on it, and then cutting up the graphic to make each frame. Worked for me.
Anything that can generate images can be used to create an animation. Once you get the frames you can stick them together with just about any graphic file manipulation program (I like GraphicConverter).