Genius.

At first this seems a little silly and then, after a second or two's reflection, turns out to be profoundly marvellous.

Google Cardboard can be made at home. It consists of a cardboard box (a large pizza box is recommended), cheap lenses, a magnet, Velcro and a rubber band combined with the Cardboard app for Android and a moderately decent smartphone (most popular modern phones will work). The result is a full stereo virtual reality (VR) experience similar to that of the Oculus Rift but at a tiny fraction of the price. It uses things like motion sensors, NFC, magnetometers and other features built into most modern smartphones to work its magic, so moving your head changes your point of view. Note the cut-out for the camera - some great potential for augmented reality (AR) apps here, blending the real world with full 3D high resolution renderings of virtual objects.

The carboard box is low-threshold enough to kick-start development using the new VR Toolkit that makes it all work. This means there will likely soon be a flood of apps for this, and it is almost certain that more polished versions of the viewer will soon start to appear on the market for those who don't want to make their own or advertise their pizza-eating habits to the world. And, assuming it takes off (which I think it should) there will then be dedicated VR glasses that make use of it. Indeed, it seems logical that this is what Google Glass will evolve into. Taking the long view, this could be an extremely disruptive innovation, providing a simple and already-available set of standards to drive VR and AR development.