This is a fantastically well-put together LibGuide listing a bunch of different apps for different subjects, includes library resources as well. I would use this as another professional development resource, have students look at sites and apps that this Christopher Bean did such a good job of organizing and compiling.
"Your two eyes each see an image and your brain takes these two images and creates one image in your mind. The eye with the red lens filter only sees the blue lines and the eye with the blue lens filter only sees the red lines. When your brain puts the two different images together in your mind it creates a 3-D image. "