We're big fans of products like the Floyd Legs, which lets you turn any slab of wood into a functional table. The Modos is a similar system that uses a series of connectors to turn erstwhile ordinary wooden boards into a variety of home furniture pieces.
Described as a "modular furniture system," it doesn't require specially-cut wood that slot into each other like giant LEGOs, the way other modular home furniture systems do. Instead, the connectors allow regular plywood boards to attach in various angles, letting you quickly build functional tables, chairs, and standing shelves without using any tools.
Rather than allow you to use any size of wood, however, the Modos connectors are designed to fit boards exactly three quarters of an inch thick. They have specific measurements for the cut sheets of individual furniture types, although you can always experiment and change up the dimensions, provided the thickness remains faithful to the original design. Constructed from aluminum, the connectors are designed to create a "friction fit" with the boards, forcing the multiple boards to, essentially, reinforce each other for inherently high structural strength.
They currently offer three types of connectors, a combination of which can be used to design stools, desks, and standing shelves according to their build plans. Chances are, you can use them to design sets of furniture beyond the pre-made plans, too (I've always wanted a modular bed frame), so you can experiment with this if you enjoy putting together original DIY furniture.
Modos is currently running a Kickstarter campaign. You can reserve connectors (with or without boards included) for pledges starting at $25.