Designed by Google but with no official manufacturer, Google Cardboard is an affordable alternative to expensive VR technology. Using a simple smartphone mount design - which comes predominantly in cardboard with some companies offering other materials such as aluminium - combined with lenses, a magnet, a piece of hook-and-loop fastener and a rubber bands. When held up to the user face it affords them a VR experience.
Although designed by Google it is not produced by them. Instead, Google has the list of parts, schematics, and assembly instructions freely available on their website, recommending people assemble one themselves from readily available parts.
The official Google Cardboard SDK uses OpenGL and the Android OS 4.1 or higher. There is an unofficial CardboardSDK iOS port.