Arduino IO Expanding Shield is very useful product which can be used with Arduino boards and designed for stacking many input and output units on board.
Arduino's all input and output pins on board are in 3-pin sequece in the order of DATA, VCC and GND. Therefore any sensor, servo, relay etc. can be stacked to the board and used easily.
Also UART and I2C ports are drawn to seperate parts on board for easy useage. Pins which are necessary for bluetooth, sd card, ultrasonic sensor and RF connection, are also drawn to seperate parts on board. There are screw terminals on board for reset button and 5V input.
There are also serial and parallel outputs on board for LCDs. LCD connection can be made with IDC cable or jumper cable.
IO Expanding Shield is completely compatible with Arduino Uno. It can be used with Leonardo and Mega versions also. But hence I2C and SPI ports are on different pins on these versions, only these ports cannot be used.