OpenCR, otherwise called the open source control module, is an STM32F7 series chip-based embedded board that is based on a very powerful ARM Cortex-M7 with a floating-point unit. It has an IMU (MPU9250) embedded on the board. It has 18 GPIO pins, 6 PWM IOs, and communication ports such as USB, a couple of UARTs, 3xRS485, and a CAN port. It has a 32-pin style berg connector like an Arduino board for connecting Arduino shields. The OpenCR board is shown here:

You can find pinout details here: http://emanual.robotis.com/docs/en/parts/controller/opencr10/#layoutpin-map. This board is used in Turtlebot 3 and the ROS package integration is pretty similar to how Arduino connects with ROS. You can have a look at how Arduino-like microcontrollers can connect with ROS here: http://wiki.ros.org/rosserial_arduino.