We often see smartly-designed furniture pieces that does double-duty; less often do we see pieces that are intended to be customized according to use, and which can arranged in an infinite number of ways. Barcelona-based design studio 5Lab's B_kube collection fits this bill though: it is made up of cube units which can be modified to function as either a seat, tray table or storage, and the units can be mixed, matched and stacked according to the situation.
For example, to create a seat, a cushion can be strapped on; to create any number of shelves with different functions, different trays of varying heights are slid in. All of these can be stacked on top of one another, using a plus-sign protrusion on the bottom, which is fitted into a cross-shaped groove, to secure it in place.
It's the kind of furniture set designed for boredom-phobic people who want to easily change their living configurations without having to move heavy shelves, as well as people with small spaces who can't fit regular-sized specimens. More images over at 5Lab.