The eight NPN Darlington connected transistors in this family of arrays
are ideally suited for interfacing between low logic level digital circuitry (such
as TTL, CMOS or PMOS/NMOS) and the higher current/voltage
requirements of lamps, relays, printer hammers or other similar loads for a
broad range of computer, industrial, and consumer applications. All devices
feature open–collector outputs and free wheeling clamp diodes for transient
suppression.
ULN2803 : Octal High Voltage, High Current Darlington Transistor Arrays
https://www.youtube.com/watch?v=pt36_inWedc