The CD4017 IC is a decade counter that counts to ten. It has 10 outputs that represent the numbers 0 to 9. The counter increases with one for every rising clock pulse. After the counter has reached 9, it starts again from 0 with the next clock pulse.
This is a great chip for making running LEDs!
 
Resources:
1. CD4017 – A Decade Counter with Decoded Output
2. CD4017 Circuits