3-D displays that don't require you to wear glasses are a devilishly tricky problem. But Microsoft's Applied Sciences Group has created a novel solution, in the form of a TV with a specially shaped lens that adjusts the image you see, depending on your viewing angle.
The TV knows where you are thanks to motion tracking software that follows exactly where your head is. Then, it calibrates a 3-D image to that specific viewing angle, and beams it through a thin, wedge-shaped lens that doubles as the TV screen. (Images are beamed into the side edge of the lens, which allows the whole assembly to be far more compact.) So far, the system can track and accommodate up to four people at a time.
The trick is that the viewing range is limited; Currently, there's only 20 degrees of freedom, though researchers think they'll be able to get that to 40 (today's LCD TVs have nearly 180-degree viewing angles).
This sort of context-aware technology is vital to creating 3-D images without glasses, because of how 3-D usually works. Stereoscopic 3-D images are made by two overlapping images colored blue and red; when our brains receive those images, they fuse them and interpret the overlap as depth.
But that means two things: You can create 3-D displays viewable only from a specific angle (like those cheap-o "holographic" stickers you grew up with), or you have to wear colored or polarized glasses that allow only one of the overlapping images to enter each eye.
For technical detail, check out the MIT Tech Review.