Kickstarter:

The Microduino series is a 100% Arduino compatible open source hardware, compatible with Arduino IDE development environment and existing Arduino sketches.

MICRODUINO IS SMALL

Microduino is small. Its size is about a quarter (25.40mm X 27.94mm / 1.0inch X 1.1inch), much smaller than the original Arduino board.

MICRODUINO IS STACKABLE

All Microduino boards adopt a uniform U-shape 27-pin standard pin-out (UPin-27). Thus Microduino series can be easily stacked together through the UPin-27, and all modules are delivered ready to stack... cont'd