This PCB has headers to plug in an Arduino Pro Micro (5 volt version) and one or two A4988 microstepping driver modules.

There is a 128x64 OLED display and a clickable rotary encoder for optional software menu options to run the system in various modes, eg. normal run mode for a given project, test mode for each motor etc.

There are 6 headers with +5v, GND, and a Pro Micro GPIO, allowing external sensors/switches or any other IO device to be connected, such as limit switches or sensors to tell software when a motor has reached a certain position.

The project is detailed on Github https://github.com/GadgetReboot/GR_StepperIO

There is also a Youtube video showing how to use this PCB to make a paper circle cutting machine:

https://youtu.be/IpUJtn2fGRE