The ULN2003 is a very versatile driver chip. It's guts contain a high voltage/high current darlington transistor array. Various different loads could be driven with this chip. A common situation is microcontrollers that need to drive relays. This can very conveniently done through the ULN2003.
DATASHEET:
https://www.google.nl/url?sa=t&source=web&rct=j&url=http://www.ti.com/lit/ds/symlink/uln2003a.pdf&ved=0ahUKEwjShojR7MXKAhUr8XIKHWm_BjQQFggeMAA&usg=AFQjCNHUdv8pRaS3Y-KFFvAIM8_JaWmeew&sig2=zABVSgwKczarZLUY6gh4vQ
