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.
Microduino configures the pinout usage table well so as to avoid any pin usage conflict between different extension modules.
We’ve benefitted from the open source community, and we’re dedicated to giving back. The Microduino is a totally open source hardware product. you can get all of our hardware design files (schematic, board design) and firmware from Microduino WIKI http://wiki.Microduino.cc
MICRODUINO IS CHEAP
Once you upload an Arduino compatible program onto the Microduino, you don’t need Microduino-FT232R anymore. You can just put Microduino-Core into your system. One -FT232R module can be reused in different applications.
Also there are various Microduino pin-out compatible (UPin-27) extension modules available with low price (check details below), which decreases prototyping and production cost.
For more detail: Arduino in your pocket, small, stackable, smart