This website is a great way to stop art block. It really challenges your mind by honing your skill of creativity. I've used it a couple of times when I was stuck with high motivation to draw but no ideas. It can range from personifying a number to drawing the universe in a box. It's very challenging and fun to do with friends to see how your mind differs from theirs.
I've used this site multiple times for class. You can pick any pose you want the character to be in and rotate to see all sides of the figure. The models are 3D and show the muscles of the body so it's perfect for anatomy class. The models they have are females, males, children, and body building figures. Using this site as a reference in my art has helped me tremendously if I needed a certain body type, age, or gender for an illustration.