You can see the Arduino-like components at the left side - 5V regulator, ICSP header for a bootloader, L LED, the microcontroller and its crystal and caps, IO headers including +5/Gnd/IO pin for connecting potentiometers or other devices that might need power), Power LED, and on this board a couple of discrete transistors - and to the right a bank of up to 12 Open Drain Shift Registers (TPIC6B595)