Bloxes: Cardboard Modular Building Blocks

Bloxes, pl. n, \ˈbläks-es\ Building blocks made of interlocking pieces of corrugated cardboard, folded together. Their unique shape and structure make them exceptionally strong and lightweight — you could build yourself a platform to stand on, and then pick it up and move it wherever you need to.

From CNET: "Bloxes are the latest option in cardboard furniture, which is gaining a toehold in the world of 'green' design. The corrugated cardboard puzzle pieces lock together to form sturdy shapes such as chairs, walls, and play forts."