This is a version 3.1 boards as supplied by BitsFromBytes. It contains a perfboard addition connected to the Sub-D 25 connector. It has an SD card slot SPI interface, USB connector and a 12 V header. It has an OLED screen and pushbuttons to control it. It runs standalone from an SD card, you don't need a computer to do 3D prints.
You can run custom firmware on it. For more information, see RapManFirmwareDevelopment.