Proto X isn't just a concept, but rather a real gadget that's touted as the world's smallest quadcopter. The 1.8" x 1.8" Proto X is tiny, ideal for indoor flying - and it weighs only four-tenths of an ounce. Bright, built-in LEDs make it easy to see the Proto X in low-light conditions. Product page.
A 2.4GHz radio not only allows for interference-free flight - it makes it easy for multiple Proto X helis to fly at once. A 3.7V 100mAh LiPo battery, USB charge cord and spare rotor blades are also included in the ready-to-fly package. All you need to add are two "AAA" batteries. More information.