We're at a stage in human scientific advancement where Tetris in 3D isn't that mind-blowing. But Tetris in 3D using water, that's impressive.
Researchers at Carnegie Mellon University have found a way to create three-dimensional images using a projector and layers of water droplets. The water drops in curtains, while the projector switches up what's being displayed on each layer, creating volumetric 3D that, because it exists in actual 3D space and not on a screen, doesn't even need glasses.
Water droplets create multilayered display [New Scientist]