It is a buffer follower. It acts just an op-amp would in the same configuration. It is used to clean up a digital signal.
Lets say that a digital driver sets its output at 5V. Then due to the traces, or due to wires, the volatge drops. If it drops far enough, then a reciever (another gate) might not respond. So, this is placed to raise the voltage back up. Take a look at buffer follower for op-amps. Red