In some situations you may want your Arduino-based project to have more I/O pins - however you may not have a spare Arduino Mega or compatible laying about, but do have an Uno or compatible. Or even a barebones Arduino via an ATmega328P with Arduino bootloader. In these cases you can now control the second Arduino from the first via the I2C bus and the ExtraCore library by Dustin Andrews.
This allows you to control the digital and analogue I/O pins of the second Arduino, including PWM and setting the inbuilt pull-up resistors - all from the main control Arduino. It's a neat way to extend the available I/O of an Arduino without worrying about complex data buses or creating your own command system and protocol. To get started, download the ExtraCore library from Dustin's github. And for more, we're on twitter and Google+, so follow us for news and product updates as well.